U.S. patent application number 12/251723 was filed with the patent office on 2009-02-05 for network overload detection and mitigation system and method.
This patent application is currently assigned to Prolexic Technologies, Inc.. Invention is credited to Barrett Lyon.
Application Number | 20090037592 12/251723 |
Document ID | / |
Family ID | 36126944 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090037592 |
Kind Code |
A1 |
Lyon; Barrett |
February 5, 2009 |
NETWORK OVERLOAD DETECTION AND MITIGATION SYSTEM AND METHOD
Abstract
Systems and methods are provided for detecting and mitigating
overload conditions affecting one or more computers attached to a
network, such as overloads resulting from distributed denial of
service (DDoS) attacks, for example. According to some described
embodiments, an attempted overload condition is detected, e.g., by
a system, through following a method, or both, within a data
cleaning center. Detection may be achieved, e.g., by analyzing data
packets traveling over the network to identify packets that bear
characteristics that may be associated with DDoS attacks, and this
analysis may include examination of the packets' data payloads.
Mitigation, in turn, may include discarding some data packets,
redirecting network traffic, or some combination thereof.
Inventors: |
Lyon; Barrett; (Sacramento,
CA) |
Correspondence
Address: |
FROMMER LAWRENCE & HAUG
745 FIFTH AVENUE- 10TH FL.
NEW YORK
NY
10151
US
|
Assignee: |
Prolexic Technologies, Inc.
Hollywood
FL
|
Family ID: |
36126944 |
Appl. No.: |
12/251723 |
Filed: |
October 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10956721 |
Oct 1, 2004 |
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12251723 |
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Current U.S.
Class: |
709/228 |
Current CPC
Class: |
H04L 29/06027 20130101;
H04L 65/103 20130101; H04L 63/02 20130101; H04L 65/1069 20130101;
H04L 65/104 20130101; H04L 65/80 20130101; H04L 63/1458 20130101;
H04L 63/1416 20130101 |
Class at
Publication: |
709/228 |
International
Class: |
G06F 15/173 20060101
G06F015/173 |
Claims
1. A system for detecting and mitigating an attempted overload
condition targeting a domain name server, comprising: a network
connection for receiving a plurality of DNS requests from one or
more client computers located on a network, the plurality of DNS
requests directed to a DNS server; and a processor for providing a
response to the plurality of DNS requests to the one or more client
computers, instead of the DNS server, if the processor detects that
a threshold number of the plurality of DNS requests received over a
time period are substantially duplicate.
2. The system of claim 1, wherein the processor discards any of the
DNS requests that are not directed to port 53.
3. The system of claim 1, wherein the processor discards any DNS
request that does not pass a DNS sanity check.
4. The system of claim 1, wherein the processor discards each
request containing a domain name that is not on a list as a valid
domain name.
5. The system of claim 1, wherein the processor detects whether a
threshold number of DNS requests are duplicate by storing the
received requests in a database, counting the number of requests
for a domain name from the same source to produce a hit count over
a period of time, and comparing the hit count against a threshold
value.
6. The system of claim 5, wherein the processor detects whether a
threshold number of DNS requests are duplicate for two or more
domain names to produce a hit count over a period of time for each
of the two or more domain names.
7. A system for detecting an attempted overload condition targeting
a networked computer system, comprising: a network connection for
receiving a data packet having an HTTP header; and an attack
detection module to determine whether a user agent header entry in
the HTTP header contains a non-alphabetical character.
8. The system of claim 7, further comprising an attack mitigation
module to discard the data packet if the user agent header entry
contains a non-alphabetical character.
9. A system for detecting an attempted overload condition targeting
a networked computer system, comprising: a network connection for
receiving a data packet having an HTTP header; and an attack
detection module to determine whether a host value header entry
exists in the HTTP header.
10. The system of claim 9, wherein the attack mitigation module
discards the data packet if the host value header entry does not
exist in the HTTP header.
11. A system for detecting an attempted overload condition
targeting a networked computer system, comprising: a network
connection for receiving a data packet; and an attack detection
module to determine whether the contents of the data packet include
a valid line break indicator.
12. The system of claim 11, further comprising an attack mitigation
module to discard the data packet if the contents of the data
packet do not include a valid line break indicator.
13. A system for mitigating an overload condition targeting a
networked computer system, comprising: a network connection for
receiving a plurality of data packets from one or more first
computers located on a network, the data packets including a
plurality of GET commands directed toward one or more second
computers located on the network; and an attack mitigation module
to determine whether a number of duplicate GET commands that have
been received-exceeds a threshold value.
14. The system of claim 13, wherein the attack mitigation module
blocks the duplicate GET commands if the threshold value is
exceeded.
15. The system of claim 13, wherein the attack mitigation module
performs a hash function on the received GET commands to determine
if the GET commands are duplicates.
16. A system for preventing an attempted overload condition
targeting a networked computer system, comprising: a network
connection for receiving one or more initial data packets from one
or more first computers for processing by a second computer; a
redirection module to redirect the first computer to send the one
or more initial data packets to a third computer; an attack
detection module to determine whether the one or more initial data
packets are a part of an attempted overload condition; and wherein
the redirection module redirects the one or more first computers to
send one or more subsequent data packets directly to the second
computer if the attack detection module determines that the initial
data packets are not a part of an attempted overload condition.
17. The system of claim 16, wherein the domain name of the third
computer has a different prefix than the domain name of the second
computer.
18. The system of claim 17, wherein the domain name of the second
computer has a prefix of www, and the domain name of the third
computer has a prefix of wwwn, wherein n is a numeric value.
19. The system of claim 16, wherein the attack detection module
determines whether the one or more initial data packets are a part
of the attempted overload condition by determining whether the
network connection has received the one or more initial data
packets from one or more browsers executing on the one or more
first computers.
20. The system of claim 19, wherein the attack detection module
determines whether the network connection has received the one or
more initial data packets from one or more browsers executing on
the one or more first computers by attempting to write one or more
cookies to the one or more first computers.
21. The system of claim 19, wherein the attack detection module
determines whether the network connection has received the one or
more initial data packets from one or more browsers executing on
the one or more first computers by providing a representation of
text, in a non-machine readable format, to be typed into the one or
more browsers by one or more users.
22. A system for preventing an attempted overload condition
targeting a networked computer system, comprising: a network
connection for receiving one or more initial data packets from one
or more first computers for processing by one or more second
computers; a redirection module to redirect the one or more first
computers to send the one or more initial data packets to one or
more third computers; an attack detection module to determine
whether the one or more initial data packets are a part of an
attempted overload condition; and wherein the redirection module
redirects the one or more first computers to send one or more
subsequent data packets directly to the one or more second
computers if the attack detection module determines that the
initial data packets are not a part of an attempted overload
condition.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a system and method for preventing
distributed denial of service (DDoS) attacks, or the like, via a
network, such as the Internet. In particular, the invention relates
to a data cleaning center having attack detection and/or mitigation
modules that provide DDoS attack-free data to back-end servers.
BACKGROUND OF THE INVENTION
[0002] During the past few decades, the Internet has provided a
convenient way to obtain a wealth of information on almost any
subject. Many paid and free information services may be offered
over the Internet, including electronic mail, home shopping,
gaming, paperless billing services, and the like. Users merely need
to obtain a web page address or uniform resource locator (URL) for
the service they desire.
[0003] In this regard, commercial revenue for Internet-based
operations has steadily increased, even for those companies that
offer their Internet services for free. The companies that offer
free services may obtain revenue from related non-Internet services
offered to their customers or through advertising on their web
site. For example, many banks offer free on-line banking services
to their account holders. Further, the most popular Internet search
engine providers charge for advertising on their search engine web
sites, which are accessed by millions of Internet users every
day.
[0004] However, as the customer base for on-line services has grown
dramatically over the years, so have the opportunities for those
who wish to engage in malicious activity targeting Internet web
sites. What originated as several individuals, or hackers, breaking
into systems for unauthorized viewing of information or sending
individual virus attacks against selected systems just for the
thrill of doing so, has evolved into extortion-based, multi-front,
attacks on many systems or whole sub-networks within the
Internet.
[0005] For example, many offshore extortionists have developed ways
to extract significant revenue from companies located in multiple
jurisdictions. These extortionists avoid prosecution by law
enforcement by launching their malicious attacks from countries in
which they may avoid prosecution, either legally or practically.
Further, the extortionists may obfuscate their identities by
launching attacks from different computers at different
locations.
[0006] Typically, an extortionist pre-warns a web site owner before
an attack, demanding that a sum of money is wired to an anonymous,
foreign account. For example, in the case of a gaming web site, the
extortionist may wait until just before a significant event, such
as an on-line poker tournament, or in the case of gambling, a major
horse race, such as the Kentucky Derby. An electronic mail message
may be sent to the site owner with the warning and appropriate bank
account information. If the site owner does not pay the amount
requested by the extortionist, then the extortionist may cause an
attack to occur at the peak time for usage of the web site during
the event. Still an attack may essentially shut down operations for
the site. Acknowledging that the threat is real, the site owner
will likely pay a potentially significant sum of money, rather than
risk the loss of a significant profit obtained during the special
event or peak time of the year.
[0007] The methods available to the extortionist are many. For
example, one type of malicious attack that may target a system is
called a distributed denial of service (DDoS) attack. This type of
attack is universally acknowledged as being one of the most
troublesome types of attacks of our time. A DDoS attack includes
"flooding" a host computer or network with information. The flood
of information can consume all available bandwidth of the host
computer's or network's computing resources, thereby preventing
legitimate network traffic from reaching the host network and
further preventing an individual user from accessing the services
of the host network. More particularly, the attacker can consume
bandwidth through a network flood either by generating a large
number of data packets, which contain data exchanged over the
Internet, or by generating a small number of extremely large
packets, directed to the target computer or network. Typically,
those packets comprise Internet Control Message Protocol (ICMP)
packets, User Datagram Protocol (UDP) stream attack packets, TCP
SYN flood packets, or packets used in TCP based attacks such as GET
flood attacks that typically occur after handshaking is completed
and a session is started. In principle, however, the packets can
include any form.
[0008] The attacker can execute the flood attack from a single
computer. This comprises a non-distributed or conventional denial
of service (DoS) attack. Alternatively, during a DDoS attack, the
attacker coordinates or co-opts several computers on different
networks to achieve the same effect. The attacker also can falsify
(spoof) the source IP address of the packets, thereby making it
difficult to trace the identity of the computers used to carry out
the attack. Spoofing the source IP address also can shift attention
onto innocent third parties.
[0009] An attacker also may execute a more defined attack using
spoofed packets called a "broadcast amplification" or a "smurf
attack." In this common attack, the attacker generates packets with
a spoofed source address of the target. The attacker then sends a
series of network requests using the spoofed packets to an
organization having many computers. The packets contain an address
that broadcasts the packets to every computer within the
organization. Every computer within the organization then responds
to the spoofed packet requests and sends data on to the target
site. Accordingly, the target computer or network becomes flooded
with the responses from the organization. Unfortunately, the target
site then may blame the organization for the attack.
[0010] Further, recent attacks have been launched against domain
name service (DNS) servers. DNS servers are essential to the
operation of the Internet, as they provide the key function of
converting alphanumeric domain names, such as XYZ.com, into the
number based Internet protocol (IP) addresses on which each
Internet connection is ultimately based. Attackers have discovered
a new way to bring down whole segments of the Internet by attacking
the DNS servers themselves, instead of the computers that the IP
addresses identify.
[0011] To date, systems for detecting and mitigating DoS or DDoS
attacks have been few. Some prior systems or solutions have
individually used or proposed different tools or software,
sometimes in the form of so-called firewalls, in an attempt to
combat such attacks. These tools or software may include: systems
that detect half-open connections that are typically caused by many
attacks; systems that compare headers of packets to specific, known
flood attack headers; or systems that monitor data packet flow that
is above average or that exceed various thresholds.
[0012] However, while these prior systems have experienced some
success, such success has been limited. For example, typical
systems attempt to prevent attacks from one or more computers, each
of which having one source, and each targeted toward a single
computer. These prior systems typically require identification of
the source computers involved in the attacks, as well as the
target, to compare duplicate source and target values to threshold
values at the network or lower layers of the open system
interconnect (OSI) model. If the attack detection tools are
successfully spoofed at lower levels of the OSI model, this leaves
higher levels of the OSI model, such as the application layer,
vulnerable to subsequent attacks. This is true, because the prior
systems assume that the data passing through a connection is safe
after it has passed through the tools at the lower layers.
[0013] Thus, none of the prior systems provide for reliable
universal protection of many computer systems or nodes through one
access point, regardless of the source and target of an attack.
Further, none of the prior systems provide for reliable universal
protection of several computer systems or nodes at the same time,
or after a connection has been deemed as safe using typical tools
at lower levels of the OSI model.
[0014] Finally, none of the prior systems provide for reliable
protection of DNS servers to prevent whole networks from becoming
non-operational. Accordingly, there is a need in the art for a
system and method that solves the problems associated with such
prior systems.
SUMMARY OF THE INVENTION
[0015] Briefly, and in general terms, a preferred embodiment
relates to a system and method for detecting and/or mitigating an
overload condition from one or more first computers, such as a
distributed denial of service (DDoS) attack, viral attack or the
like, targeting one or more of a plurality of second computers
located on a network. The network may comprise any type of public
or private network, such as the Internet, intranet, virtual private
network (VPN) or the like. While one or more DDoS attacks
originating from the one or more first computers on the network are
mitigated, a meter, detection apparatus, software, or method,
detects the condition being mitigated in a data cleaning center,
and in one embodiment, it provides an alert or notification
regarding the mitigated attack.
[0016] A preferred embodiment comprises a data cleaning center,
preferably as a stand-alone node on the network, which has a
network connection for receiving a volume of data, and which may be
measured as D.sub.in, over a time period, P.sub.in. The data may be
received from, for example, one or more first computers located on
the network.
[0017] The overload condition is directed to one more of a
plurality of second computers located on the network. Typically,
the second computers are server computers, and the first computers
are client or user computers. However, a preferred embodiment does
not necessarily differentiate between client and server computers
in detecting and mitigating the overload condition. Thus, each of
the first and second computers may comprise a server, client,
networked electronic device, or any type of network node.
Sometimes, for example, an attempted overload condition in the form
of a SYN-flood attack may be launched from several different
computers, including servers and clients, that are unwittingly
infected with a SYN-flood virus.
[0018] One embodiment includes one or more attack detection and/or
mitigation modules that are used for detecting and/or mitigating
the attempted overload condition. One purpose of the attack
detection and/or mitigation modules is to produce a volume of data
that is free from the data causing the overload or attempted
overload condition, called clean data, or D.sub.out, herein, for
sending to the one or more second computers. The amount or volume
of the clean data may be measured as D.sub.out, over a time period,
P.sub.out.
[0019] In one embodiment, a meter is included to perform the task
of measuring D.sub.in and D.sub.out and for comparing such
measurements to determine whether the attempted or actual overload
condition has been mitigated by the attack detection and/or
mitigation modules. The meter determines that such an attempted or
actual overload condition directed toward one or more of the second
computers has been mitigated if D.sub.out divided by P.sub.out is
substantially less than D.sub.in divided by P.sub.in.
[0020] One embodiment includes an alert apparatus to provide an
alert if the meter detects an overload or attempted overload
condition. The alert apparatus may provide an electronic mail
alert, an audible alert, a visible alert, or the like, if an
attempted overload condition is detected by the meter.
[0021] In one embodiment, the one or more attack detection and/or
mitigation modules include a module that determines whether a
number of duplicate GET commands have been received that exceeds a
threshold value. Another attack mitigation module may also include
a module that determines whether a user agent header entry in a
packet header of a received data packet contains an alphabetical
character. If not, the data packet is discarded. Further, one
attack detection/and or mitigation module is included that
determines whether a host value header entry exists in a packet
header of a data packet, and if not, discards the data packet.
[0022] Another preferred embodiment relates, in general terms, to a
system and method for detecting and/or mitigating an overload or
attempted overload condition targeting a domain name service (DNS)
server. A network connection is provided for receiving one or more
DNS requests from one or more client computers located on a
network. A preferred embodiment includes a processor for providing
a response to the one or more DNS requests to the one or more
client computers before normal processing by the domain name
server.
[0023] The added processor preferably executes processes used to
detect whether the one or more DNS requests comprise an attempted
overload condition before allowing processing of the requests by
the domain name server. If an overload or attempted overload
condition is detected by the processor, then processing by the
domain name server of the DNS requests is performed by the
processor. Specifically, the requests are diverted to the
processor, which comprises high-speed application specific hardware
that can process requests much faster than typical DNS servers.
Once the overload condition or attempted overload condition has
subsided, processing of the requests are re-diverted back to the
DNS server.
[0024] Another preferred embodiment relates, in general terms, to a
system and method for detecting and/or mitigating an attempted
overload condition targeting a networked computer system by
counting a number of duplicate GET commands received. A network
connection is provided for receiving a plurality of data packets
from one or more first computers located on a network, wherein the
data packets include a plurality of GET commands directed toward
one or more second computers located on the network. An attack
detection and/or mitigation module is provided that comprises a
module to compare the received GET commands, and to determine
whether a threshold number of the received GET commands are
duplicative. If the threshold value is exceeded by the duplicate
GET commands, then the attack mitigation module blocks or discards
the duplicate GET commands from processing by the one or more
second computers.
[0025] Due to the large volume of GET commands that may be
received, a database function may be performed on the received GET
commands to determine if the GET commands are duplicates. The
database function may include a hashing algorithm applied to the
GET commands to speed processing and to use less memory.
[0026] Another preferred embodiment relates, in general terms, to a
system and method for detecting and/or mitigating an attempted
overload condition targeting a networked computer system that
checks the user agent header entry of a packet header. A preferred
embodiment includes a network connection for receiving a data
packet having a packet header. An attack detection and/or
mitigation module is provided to determine whether a user agent
header entry in the packet header contains an alphanumeric
character. Thus, the attack detection and/or mitigation module
discards the data packet if the user agent header entry contains a
non-alphanumeric character. Further, patterns in the user agent
entry and/or other header entries may be detected that may indicate
an attack.
[0027] Another preferred embodiment relates, in general terms, to a
system and method for detecting and/or mitigating an attempted
overload condition targeting a networked computer system that
checks the host value header entry of a packet. A network
connection is provided for receiving a data packet having a packet
header. An attack detection and/or mitigation module determines
whether a host value header entry exists in the packet header. The
attack detection and/or mitigation module discards the data packet
if the host value header entry does not exist in the packet
header.
[0028] Another preferred embodiment relates, in general terms, to a
system and method for detecting and/or mitigating an attempted
overload condition targeting a networked computer system that
checks line break indicators in packets. A network connection is
provided for receiving a data packet. An attack detection and/or
mitigation module determines whether the data packet contains valid
line break indicators. An example of a non-valid line break
indicator is one that only contains one of a carriage return
character (CR) or a line feed character (LF), and not both. The
attack detection and/or mitigation module discards the data packet
if the data packet does not contain a valid line break
indicator.
[0029] Another preferred embodiment relates, in general terms, to a
system and method for detecting and/or mitigating an attempted
overload condition targeting a networked computer system that uses
a redirection module to divert data until it is deemed to be clean.
A network connection is provided for receiving one or more initial
data packets from one or more first computers for processing by a
second computer. A redirection module redirects the first computer
to send the one or more initial data packets to a third computer.
An attack detection and/or mitigation module determines whether the
one or more initial data packets are a part of an overload or
attempted overload condition. The redirection module then redirects
the one or more first computers to send one or more subsequent data
packets directly to the second computer if the attack detection
and/or mitigation module determines that the initial data packets
are not a part of an attempted overload condition. Otherwise, the
data from the one or more first computers remains redirected to the
third computer. These and other aspects of the invention will
become apparent from the following more detailed description, when
taken in conjunction with the accompanying drawings of illustrative
embodiments.
DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a block diagram of a data cleaning center
according to an exemplary embodiment of the system and method for
detecting and/or mitigating an overload or attempted overload
condition;
[0031] FIG. 2 is a block diagram illustrating packet switching flow
through various hardware components of the data cleaning center
according to another exemplary embodiment;
[0032] FIG. 3 is a flow diagram illustrating the steps performed by
one or more embodiments of the data cleaning center;
[0033] FIG. 4 is a flow diagram illustrating a method performed by
one exemplary embodiment of an attack mitigation module for
detecting an attack based on whether a suspect number of duplicate
GET commands are received over a sample time period;
[0034] FIG. 5 is a flow diagram illustrating a method performed by
one exemplary embodiment of an attack mitigation module for
detecting and/or mitigating an attack by discarding data packets
that have packet headers with a suspect user agent entry;
[0035] FIG. 6 is a flow diagram illustrating a method performed by
one exemplary embodiment of an attack mitigation module for
detecting and/or mitigating an attack by discarding data packets
that have packet headers with suspect host value entries;
[0036] FIG. 7 is a flow diagram illustrating a method performed by
one exemplary embodiment of an attack mitigation module for
detecting and/or mitigating an attack by discarding data packets
that use improper end-of-line or return characters;
[0037] FIG. 8 illustrates a method for preventing an attempted
overload condition targeting a networked computer system that
lessens or eliminates the latency effect of using the data cleaning
center, such as that illustrated in FIG. 1;
[0038] FIG. 9 is a block diagram of a DNS protection system
according to an exemplary embodiment; and
[0039] FIG. 10 is a flow diagram that illustrates a method
preformed by the DNS protection system.
DETAILED DESCRIPTION
[0040] A preferred embodiment of a system and method for detecting
and/or mitigating an overload condition, constructed in accordance
with the claimed invention, provides detection and/or mitigation of
an overload condition style attack from one or more first computers
that target one or more of a plurality of second computers located
on a network. Such attack includes, by way of example only, and not
by way of limitation a distributed denial of service (DDoS) attack,
viral attack or the like. The network may comprise any type of
public or private network, such as the Internet, intranet, virtual
private network (VPN) or the like.
[0041] Referring now to the drawings, like reference numerals
denote like or corresponding parts throughout the drawing
figures.
[0042] Referring now to FIG. 1, a preferred data cleaning center
100 is illustrated, according to an exemplary embodiment of the
system and method for detecting and/or mitigating an overload or
attempted overload condition (hereinafter "an attack"). In a
preferred embodiment, the data cleaning center 100 operates as a
stand-alone node on a network 10, which has a network connection
126 for receiving a volume of data, which is measured as D.sub.in,
over a time period, P.sub.in. The network connection 126 comprises
a core edge aggregation router 102 to provide a backbone connection
to the network 10. Core edge aggregation routers 102 that are
available from, for example, Juniper Networks or Cisco Systems, are
able to provide Internet connections of 76 gigabits per second or
larger. In one embodiment, the data cleaning center 100 is
configured to provide attack free, or clean, data to hundreds or
thousands of servers, a core edge aggregation router 102 having a
capability in the 1 to 76 gigabit per second range is desirable,
although not necessary.
[0043] Through the network connection 126, data may be received
from, for example, one or more first computers 20a, 20b and 20c
located on the network 10. Typically, the one or more first
computers 20a, 20b and 20c comprise client computers or devices
used by Internet users for accessing one or more second computers
80a, 80b 80c and 80d also located on the network 10. In one
embodiment, it is preferable for all data to pass through the data
cleaning center 100. In other words, both requests and responses to
and from servers preferably pass through the data cleaning center
100.
[0044] Preferably, the data cleaning center 100 discards all data
packets that are a part of the received data, D.sub.in, that use
User Datagram Protocol (UDP) or Internet Control Message Protocol
(ICMP). This is performed because, presently, these are common
protocols used to launch DDoS attacks against the second computers
80a, 80b, 80c and 80d. Further, many commercial networks do not
need to use UDP and ICMP protocols. The filtering of UDP and ICMP
packets may be performed by the core edge aggregation router 102.
However, if it becomes more common to use a different type of
protocol to launch attacks against the second computers 80a, 80b,
80c and 80d, then the core edge aggregation router 102 may be
re-tuned to filter and discard data packets using such protocol.
Alternatively, the core aggregation router 102 may discard all data
packets, except those having selected protocols, such as
Transmission Control Protocol (TCP).
[0045] In one preferred embodiment, a core router 108 is provided
that has or connects to, an inbound access control list (ACL) 124
for sanity checking, which typically includes confirming that the
target node is listed in the ACL. Specifically, each incoming
packet is preferably checked against the ACL, which provides a
list, or range, of valid IP addresses for the second computers 80a,
80b, 80c and 80d serviced by the data cleaning center 100. If a
data packet is not directed to, or coming from, an IP address
contained in the ACL 124, it is discarded.
[0046] In a preferred embodiment, a meter 104 is either connected
to the core router, or within the core router for measuring the
received data, D.sub.in. The meter 104 preferably operates on a
Unix-based platform or other platform, and preferably performs its
measurement of the received data, D.sub.in, from the core router
108 after the filtering of the UDP and ICMP data packets by the
core edge aggregation router 102. However, in some embodiments it
is desirable to include measurements of the UDP and ICMP data
packets received by the data cleaning center 100. In those
embodiments, the meter 104 is preferably connected to the core edge
aggregation router 102 instead of the core router 108.
[0047] After the core router 108 has completed its processing
procedures, the received data, D.sub.in, is preferably further
processed by one or more attack detection and/or mitigation tools
or modules 110 (referred to herein as attack mitigation modules).
In one embodiment, the one or more attack mitigation modules 110
are used to detect, mitigate, prevent and/or suppress one or more
DDoS attacks that originate from the one or more of the first
computers 20a, 20b and 20c on the network 10, and are directed to
the one or more second computers 80a, 80b, 80c and 80d, located on
the network 10.
[0048] Typically, the one or more second computers 80a, 80b, 80c
and 80d at which an attack is targeted, are server computers, and
the one or more first computers 20a, 20b and 20c from which an
attack originates, are client or user computers. However, a
preferred embodiment does not necessarily differentiate between
client and server computers in detecting and/or mitigating an
attack. Thus, each of the first and second computers may comprise a
server, client, networked electronic device, or any type of network
node. Sometimes, for example, an attack in the form of a SYN-flood
attack is launched from several different computers, including
servers, clients, company networks or sub-networks that are
unwittingly infected with a SYN-flood virus.
[0049] Furthermore, it may be desirable to detect and mitigate
attacks using multiple different techniques. As such, some
preferred embodiments use more than one attack mitigation module
110. In some embodiments, the attack mitigation modules 110 are
chained or combined, for example, by providing a series of
processors connected within a preferably high-speed local fiber
optic network, or attack mitigation pipe or loop 150, within the
data cleaning center 110. Preferably, the attack mitigation modules
110 are embodied in hardware, software, or via a combination of
hardware and software.
[0050] There are several types of attack mitigation modules 110
that may be used in a preferred embodiment of the claimed
invention. For example, many types of attack mitigation modules 110
are configured to detect a flood-type DoS attack, or DDoS attack.
Some modules 110 perform this type of detection by using
statistical analysis on data packets D.sub.in received from the
network 10 to determine when the data packets vary from normal
network traffic. Normal network traffic is determined based on
observations of network traffic for a particular network.
Thresholds for abnormal network traffic may be established based
upon the observations and upon a balance between security level and
false positive indications. An appropriate balance must be selected
since a lower threshold will likely result in higher security, but
may cause more false positive indications of an attack. On the
other hand, a higher threshold can result in lower security, but
with fewer false positive indications.
[0051] Preferably, after establishing the thresholds, the attack
mitigation module 110 statistically analyzes the network traffic to
determine when the traffic exceeds the thresholds. In this
embodiment, if the traffic exceeds the thresholds, an attack is
detected. After an attack is detected, countermeasures can be
initiated to block data packets from a specific IP address.
Additionally, countermeasures can be initiated to block data
packets to or from a common port, data packets having a common
protocol, and/or data packets having the same target or destination
IP address.
[0052] In some attack mitigation modules 110, a hash (or reduction)
function is performed on the data packets, the results of which are
sorted in a hash table. In such an embodiment, if the standard
deviation of the entries in the hash table meets a threshold value,
then a network attack is detected.
[0053] Preferably, some attack mitigation modules 110 can monitor a
parameter value, such as the protocols or protocol flags of network
data packets. These modules preferably construct a histogram of the
parameter value, and compare the histogram to a threshold value. In
such an embodiment, if a portion of the histogram exceeds the
threshold, then a network attack is detected.
[0054] Another preferred attack mitigation module 110 monitors the
ratio of data packets received and sent to a single computer. If
the ratio exceeds a threshold value, then a network attack is
detected. Alternatively, the attack mitigation module 110 may
monitor, for example, the ratio of traffic from a first computer
(e.g., 20a), to a second computer; e.g., 80b), over the traffic
from the second computer 80b to the first computer 20a. If the
ratio exceeds a threshold value, then an attack may be detected,
and the traffic between the first computer 20a and second computer
80b may be discarded.
[0055] In another aspect of a preferred embodiment, another attack
mitigation module 110 determines whether the attack was initiated
from a single source computer 20a, or determines whether data
packets included in an attack have a common port or protocol. If
the attack was initiated from a single source computer 20a, then
all data packets having the same attacking source IP address can be
discarded. Additionally, if the attack was initiated by data
packets having a common port or protocol, then all data packets
having the common port or protocol can be discarded. Preferably,
the attack mitigation modules 110 use other identifying
information, such as the destination address, the destination port,
or the content of the data packet itself, to determine whether a
data packet should be discarded.
[0056] Additionally, in another preferred attack mitigation module
110, the module detects an attack by determining whether a number
of duplicate GET commands have been received that exceeds a
threshold value. If the threshold value is exceeded, then the
duplicate packets are discarded. This module is described in more
detail below.
[0057] Yet another preferred attack mitigation module 110 detects
an attack by determining whether a user agent header entry in a
packet header of a received data packet contains an alphabetical
character. If an alphabetical character is not detected, the data
packet is discarded. This module is described in more detail
below.
[0058] Still another preferred attack mitigation module 110 detects
an attack by determining whether a host value header entry exists
in a packet header of a data packet. If the host value header entry
does not exist, the data packet is discarded. This module is
described in more detail below.
[0059] In yet another preferred embodiment, the attack mitigation
module 110 keeps a blacklist of source addresses. The blacklist is
created, for example, from prior recorded attacks. If a received
data packet, D.sub.in, contains a source address that is a member
of the black list, the packet is blocked or discarded. In this
regard, as attacks get more sophisticated, the attackers are able
to modify the source address in the attacking data packets.
However, even after changing the source addresses, many of the
attacks use data packets that have not changed the source server or
sub-network. The blacklist also tracks suspect servers or
sub-networks. In one preferred embodiment, the attack mitigation
module 110 discards data packets from a server or sub-networks if,
for example, more than a threshold number of attacks have
originated from the server or sub-network within the past year. It
should be noted that any time period might be used, however, for
such a determination.
[0060] Preferably, the attack mitigation modules 110 produce a
volume of data that is free of data causing the attack, called
clean data, or D.sub.out, herein, for sending to the one or more
second computers 80a, 80b, 80c and 80d. The amount or volume of the
clean data is measured as D.sub.out, over a time period,
P.sub.out.
[0061] The data cleaning center 100 may optionally include a
distribution router 112, which provides a backbone or clean pipe to
other data cleaning centers 100a, 100b, 100c and 100d following
processing by the attack mitigation modules 110. Preferably, the
backbone uses a high-speed connection 158 to directly connect each
data cleaning center 100, 100a, 100b, 100c and 100d. Providing a
connection to other data cleaning centers 100a, 100b, 100c and 100d
allows two or more data cleaning centers to share and distribute
processing. For example, some data cleaning centers have updated
attack mitigation modules 110 that preferably are remotely accessed
by other data cleaning centers that have not been updated.
[0062] Further, if a particular data cleaning center 100 has one or
more subsystems that fail, such as one or more attack mitigation
modules 110, then the attack detection and/or mitigation function
may be outsourced to a fully functioning data cleaning center
through the distribution router 112. Moreover, if one data cleaning
center 100a is overwhelmed by one or several large attacks,
processing of the one or more attacks may be load balanced across
the backbone 158 to distribute processing across the other data
cleaning centers 100, 100b, 100c and 100d.
[0063] Preferably, after the received data, D.sub.out, is processed
to produce the clean data, D.sub.out, the next task is to provide
the clean data, D.sub.out, to one or more proxy servers 116. In one
preferred embodiment, the proxy servers provide a reverse proxy
function to the one or more second computers 80a, 80b 80c and 80d.
In this case, the second computers 80a, 80b, 80c, and 80d comprise
server computers. As is typical, the proxy servers 116 provide
added protection to the second computers 80a, 80b 80c and 80d that
are server computers. For example, a firewall may be included in a
proxy server 116 that is specific to the target server. Further, a
server may also use two or more of the proxy servers 116 to provide
load balancing.
[0064] In this regard, load balancing of all of the proxy servers
116 is preferably provided using a load balancing apparatus 114.
The load balancing apparatus 114 may include, by way of example
only, and not by way of limitation, a RADWARE WSD.TM. device
produced by Radware, Inc. of Mahwah, N.J., a JUNIPER.TM. M series
device produced by Juniper Networks, Inc. of Sunnyvale, Calif. Any
other similar device may also be used.
[0065] In one embodiment, two or more of the load balancing systems
114 are provided so that different types of systems are available
for matching with the proxy servers 116 depending on specific
requirements. For example, software-based load balancing systems
114 tend to be less expensive, but slower, than hardware-based load
balancing systems 114. Further, a particular sever computer 80b
may, for example, only require that the slower software-based load
balancing system 114 is used because the server 80b has a lower
throughput of clean data, D.sub.out, than another server 80c, which
requires a faster, hardware-based, load balancing system 114
because of its higher usage.
[0066] One or more of the attack mitigation modules 110 may be
located in, or execute on, each of the proxy servers 116. It is
preferable, for example, for those mitigation modules 110 that
execute on the application layer to reside in the proxy servers 116
after the network layer packet headers have been stripped. For
example, the mitigation module 110 that checks for duplicate GET
commands is preferably located on each of the proxy servers
116.
[0067] After the clean data, D.sub.out, is routed through the proxy
servers 116, it is processed by the core router 108 for forwarding
to their destination over the network 10. The meter 104 takes a
measurement of the clean data, D.sub.out, as it is routed out to
the core edge aggregation router 102, which processes the clean
data, D.sub.out, for distribution through the network 10.
[0068] In one embodiment, while the meter 104 performs the task of
measuring D.sub.in and D.sub.out, the meter 104 further compares
the measurements to determine whether an attack has been mitigated
by the attack mitigation modules 110. For example, the meter 104
may determine that such an attack directed toward one or more of
the second computers 80a, 80b, 80c and 80d has been mitigated if
D.sub.out divided by P.sub.out is substantially less than D.sub.in
divided by P.sub.in.
[0069] In preferred embodiments of the claimed invention, there is
flexibility with regard to this implementation of the detection
method. For example, in most embodiments, wherein the time periods.
P.sub.in and P.sub.out are long enough (e.g., 10 seconds), the
measurement of the data D.sub.in and D.sub.out occurs during the
same time interval, wherein the start of time periods P.sub.in and
P.sub.out are concurrent. In these embodiments, any latency, L,
that occurs in the one or more data mitigation modules 110, proxy
servers 116, or other modules within the data cleaning center 100,
would be a matter of microseconds. Accordingly, any difference in
the measurement of D.sub.in and D.sub.out caused by the latency, L,
would be relatively minimal when compared to the data throughput of
the data cleaning center 100.
[0070] However, in configurations wherein the time periods P.sub.in
and P.sub.out are closer in duration to the latency period, L, for
processing of the received data, D.sub.in, the latency period, L,
is preferably taken into account in the detection method. In these
configurations, it may be desirable to measure D.sub.in and
D.sub.out over two different, but equal, time periods, P.sub.in and
P.sub.out, to account for the latency, L, for processing of the
received data D.sub.in by the attack detection and/or mitigation
modules. More specifically, the time period, P.sub.out, has a start
time that occurs after the start time of P.sub.in, plus a latency
time period, L, for processing of the received data, D.sub.in, by
the attack detection and/or mitigation modules. Typically, the
latency period, L, is calculated by using historical averages for
processing the received data D.sub.in by the attack detection
and/or mitigation modules 110, or other sub-systems within the data
cleaning center 100.
[0071] Another variable in the implementation of the detection
method is the measure of the value of "substantially less" with
regard to the comparison of D.sub.out divided by P.sub.out and
D.sub.in divided by P.sub.in. For example, in one embodiment, the
measure of what is "substantially less" to determine if an attack
is occurring may be an almost absolute measurement. Specifically,
D.sub.out divided by P.sub.out may be deemed substantially less
than D.sub.in divided by P.sub.in if (D.sub.in divided by P.sub.in)
minus (D.sub.out divided by P.sub.out) is greater than 0, plus or
minus a number of megabits in high-throughput systems.
[0072] However, in another embodiment, D.sub.out divided by
P.sub.out may be considered to be substantially less than D.sub.in
divided by P.sub.in if (D.sub.in divided by P.sub.in) minus
(D.sub.out divided by P.sub.out) is greater than a specified
threshold value. Preferably, the threshold value is determined from
historical averages of differences between the values of the
received data, D.sub.in divided by P.sub.in, and the clean data,
D.sub.out divided by P.sub.out, during normal, non-attack time,
operations. The differences in the values may be due to processes
in the system such as caching or the like. In this embodiment, the
use of the threshold value may also provide a method for taking
latency, L, into account in the determination as to whether there
is an attack.
[0073] In another preferred embodiment, some of the data D.sub.in
received from the one or more first computers 20a, 20b and 20c is
cached after it is cleaned. Subsequently, as is typical in many
networked systems, a portion of the received data D.sub.in is the
same as, or the duplicate of, previously received data D.sub.in. If
the cleaned version, D.sub.out, of the received data is in the
cache, then the cached clean data, D.sub.cache, is sent to the one
or more second computers 80a, 80b, 80c and 80d in lieu of a portion
of the received data, D.sub.in. In this embodiment, the cache is
mathematically taken into account in determining the meaning of
"substantially less." Specifically, the system determines that
D.sub.out divided by P.sub.out is substantially less than D.sub.in
divided by P.sub.in, if ((D.sub.out plus D.sub.cache) divided by
P.sub.out) is less than (D.sub.in divided by P.sub.in). As
described above, if the result is a non-zero value, a threshold
value is used in this embodiment to compare to the result to allow
for non-attack condition variances before an attack is determined
to have been detected.
[0074] In another embodiment, the time periods for P.sub.in and
P.sub.out do not necessary have to be equal in length, as the
comparison of the received data, D.sub.in, and clean data,
D.sub.out, is normalized due to the division by the relative time
periods, P.sub.in and P.sub.out, to provide megabit per second
(Mbit/sec) ratios that can be compared. Also in this embodiment, a
threshold value is used in the comparison of the ratios to take
into consideration non-attack condition fluctuations in data
rates.
[0075] In one embodiment, the meter 104 is more passive and merely
records the measurements of D.sub.in over P.sub.in and D.sub.out
over P.sub.out. Further, it may be preferable to provide for remote
access by a network device, such as a client computer or
workstation 90, to the data cleaning center 100 to perform any
other calculations necessary to determine if an attack is
occurring. In this embodiment, the remote workstation 90 comprises
a standard personal computer or notebook with access to the network
10. Using the workstation 90, components of the data cleaning
center 100 are preferably accessed through a secure connection
using known encryption techniques. Specifically, the remote
workstation 90 may read measurements taken by the meter 104 to
perform the determination of whether an attack is occurring. Using
such a workstation 90 provides the added advantage of allowing the
measurements from the meter 104 to be downloaded, stored, and
manipulated in various statistical software packages, such as
EXCEL.TM. by the Microsoft Corp., or OPENVIEW.TM. by the
Hewlett-Packard Development Company, L.P.
[0076] In one embodiment, an alert apparatus is provided either as
a part of the meter 104 or the remote workstation 90, to provide an
alert if an attack is detected and/or mitigated. Preferably, the
alert apparatus provides, by way of example only and not by way of
limitation, an electronic mail alert, an audible alert, a visible
alert, or the like.
[0077] Referring now to FIG. 2, a schematic block diagram of
various hardware components of the data cleaning center 100 are
shown according to another preferred embodiment. The data,
D.sub.in, is received by the core edge router 102. Such a core edge
router 102 may comprise a JUNIPER M40.TM. router produced by
Juniper Networks of Sunnyvale, Calif. Any similar device may also
be used. The core edge router 102 performs the task of filtering
the incoming data packets, D.sub.in, which comprises the discarding
of all packets using UDP or ICMP protocols. In some instances, one
of the second computers being protected by the data cleaning center
100 may require reception of UDP or ICMP packets. In those
instances, an administrator at the data cleaning center 100 sets
the core edge router 102 so that UDP or ICMP data packets received
for the particular second computer are allowed to pass through the
data cleaning center 100. Nevertheless, the attack mitigation
modules 110 described herein can sufficiently protect the second
computer 80 receiving UDP and ICMP packets from various
attacks.
[0078] Preferably, the core router 108 is, by way of example only,
a BIG IRON.TM. 4000 router available from Foundry Networks of San
Jose, Calif., which provides network layer three packet switching.
In some embodiments, more than one router is used to perform the
functions of the core router 108. For example, one BIG IRON.TM.
4000 system may be used to process the received data, D.sub.in, and
another may be used to process the clean data, D.sub.out.
[0079] From the core router 108, the received data, D.sub.in, may
pass through the meter 104. In one preferred embodiment, the meter
104 comprises, by way of example only, a NET IRON 800.TM. monitor,
which provides a gigabit layer three switch that can monitor the
received data, D.sub.in. As stated above, the meter 104 also may be
configured to monitor the clean data, D.sub.out that is outgoing
back to the network 10 after passing through the other components
of the data cleaning center 100. In this way, the meter 104
provides a "mirrored image" observation of data D.sub.in, being
received by the data cleaning center, and the corresponding clean
data, D.sub.out, being produced by the data cleaning center
100.
[0080] In one preferred embodiment, over and above the measurement
of D.sub.in verses D.sub.out, the NET IRON 800.TM. performs some of
the functions of the data mitigation modules 110. For example, a
SYN-flood attack detector may be included in the meter 104. The
meter 104 sorts and counts the received data packets, D.sub.in,
according to their sources and destinations, and count the number
of packets marked with an "S" for send packets verses the number of
other types of packets over the same period of time, P.sub.in, such
as acknowledge (ACK) packets. If the number of send packets over
other types of packets is more than a threshold, for example, 20%
more, then a possible attack may have been detected, and an alert
may be provided by the alert apparatus.
[0081] In some situations, however, it is preferable to use
dedicated computer hardware systems on the local fiber network 150
to perform the attack detection and/or mitigation functions. For
example, one of the attack mitigation modules 110 may comprise, by
way of example only, and not by way of limitation, an ATTACK
MITIGATOR IPS 2800.TM. or ATTACK MITIGATOR IPS 5500.TM., which are
each available from Top Layer Networks of Westborough, Mass. The
ATTACK MITIGATOR IPS 5500.TM. blocks HTTP worms and other hybrid
threats, using advanced "normalized" deep packet and multi-packet
HTTP URL matching and wildcard checking, and is pre-configured to
identify hundreds of HTTP URL exploits, including DoS and DDoS
attacks, and trojan horses.
[0082] In another preferred embodiment, one ATTACK MITIGATOR
IPS.TM. 5500 contains several or all of the attack mitigation
modules 110. However, two or more of the ATTACK MITIGATOR IPS
5500.TM.s, shown as 110a, 110b, 110c and 100d in FIG. 2, are
duplicated in the local fiber network 150 to allow load balancing
to provide higher output. Open Shortest Path First (OSPF) routing
protocol also may be used, and is able to determine if a link to an
attack mitigation module 110a or 110b in the local fiber network
150 is down, so that the received data, D.sub.in, may be re-routed
to other attack mitigation modules 110c or 110d performing the same
function.
[0083] Another router 130 may be used to re-aggregate the load
balanced data, D.sub.in, which, for the most part, is characterized
as clean data, D.sub.out, when it reaches the router 130. Another
NET IRON 800.TM., or NET IRON 400.TM. offered from the same
manufacturer, may be used to perform this function. In some
embodiments, the router 130 may comprise an aggregate of several
routers 130a and 130b.
[0084] Optionally, further attack mitigation modules 110e and 110f
are used after re-aggregation of the data. For example, the attack
mitigation modules 110e and 110f preferably comprise available
firewall systems to further ensure that the data, D.sub.out, is
free of data packets sent as part of an attack. If the firewalls
110e and 110f are load balanced, then a router 160, such as a
NetIron 800 or 400 may be used to re-aggregate the data. In higher
volume systems, the re-aggregation process may be split between two
or more routers 160a and 160b.
[0085] After the clean data, D.sub.out, is re-aggregated, it is
ready to be load balanced and apportioned to proxy servers 116. In
the embodiment shown in FIG. 2, the load balancing apparatus 114
comprises a cluster of load balancing systems 114a and 114b. In one
embodiment, each load balancing system of the cluster 114
comprises, by way of example only, one of the aforementioned
RADWARE WSD.TM. devices, Foundry SERVER IRON.TM. devices, and Dell
POWEREDGE.TM. devices. The brand selection of each of the load
balancing devices 114a and 114b mainly depends on the number of
proxy servers serviced by the device and the total throughput
required. For example, some hardware-based systems, such as the
RADWARE WSD.TM. device, operate faster than some software based
systems, such as the Foundry SERVER IRON.TM. device.
[0086] Preferably, the clean data, D.sub.out, is then transmitted
over the local network 150 back to the core router 108, and then
core edge router 102. The proxy servers 116 may be divided into
clusters, wherein the proxy servers within each of the clusters are
load balanced by one of the load balancing devices 114.
[0087] As described with respect to FIG. 1, one or more of the
attack mitigation modules 110 may be executed on each of the proxy
servers, as symbolically shown as 110g in FIG. 2.
[0088] In some embodiments, each and every component illustrated in
FIG. 2 may either be combined into one processor or computer that
has multiple processors, and/or software processors, to process the
functions described above. In other embodiments, the processing for
all, or at least some of, the components may be expanded across
multiple hardware devices for processing in parallel. As an
example, in some embodiments, only one load balancing device 114
may be required if only a few proxy servers 116 are needed in the
data cleaning center 100. Further, the proxy servers 116 may be
combined into one multiplexing device that provides proxy services
for several servers.
Methods Performed by the Data Cleaning Center
[0089] Referring now to FIG. 3, a flow diagram is shown that
illustrates the steps performed by one or more exemplary preferred
embodiments of the data cleaning center 100. Specifically, the flow
diagram illustrates the steps performed in a method for detecting
and mitigating an attack, overload condition, or attempted overload
condition (collectively referred to as an "attack") that may
originate from one or more first computers, targeting one or more
of a plurality of second computers located on a network. A volume
of data, D.sub.in, is received over a time period, P.sub.in, from
one or more first computers located on a network, step 300. The
data packets of the received data, D.sub.in, is filtered to discard
data packets using UDP and ICMP protocols, with the exception that
the UDP and ICMP packets directed to destination addresses
requiring those protocols are not discarded, step 302. The
remaining received data packets, D.sub.in, are measured by the
meter over a time period, P.sub.in, step 304.
[0090] The received data packets, D.sub.in, are processed through
the attack mitigation modules to detect and mitigate the attack,
step 306, to produce a volume of clean data, D.sub.out, over a time
period, P.sub.out, wherein the time period, P.sub.out, may be equal
to the time period, P.sub.in. The clean data, D.sub.out, is load
balanced, step 308, and processed by the proxy servers, step 310.
The clean data, D.sub.out, over the time period, P.sub.out, is
measured, step 312. The presence or absence of the attack targeting
the one or more second computers is determined by calculating
whether D.sub.out divided by P.sub.out is substantially less than
D.sub.in divided by P.sub.in, step 314. Finally, the clean data,
D.sub.out, is distributed over the network to the one or more
second computers, step 316.
[0091] Referring now to FIG. 4, a preferred embodiment method is
shown of an attack mitigation module for detecting an attack, based
on whether a suspect number of duplicate GET commands, or commands
requesting the same information, are received from one or more
first computers targeting one or more second computers on a network
over a sample time period. However, it should be noted that
duplicates or patterns in the header may also be detected by this
method.
[0092] The attack mitigation module may be included for use in a
data cleaning center protecting a plurality of computer systems,
such as that shown in FIG. 1. Preferably, the method of FIG. 4 is
executed on each of the proxy servers (116 of FIG. 1). However, the
attack mitigation module may be used in a stand-alone device or
computer system on the network to protect one or a few server
computers, and may be implemented in software, hardware, or in a
programmable logic chip, such as an application specific integrated
circuit (ASIC), field programmable gate array (FPGA), or the
like.
[0093] A network connection (e.g., the network edge router of FIG.
1), receives a plurality of data packets, wherein many of the data
packets may comprise GET commands, from the one or more first
computers located on the network, step 400. Each GET command is
stored in a database for a period of time, step 402, which is
preferably determined according to a statistical history of the
length of time needed to collect a sufficient number of GET
commands to sample, and the capacity of the storage device used to
store the GET commands. For example, for a system processing up to
10 gigabits per second, and having a network storage device with a
capacity of two or more hundred gigabytes set aside for the attack
mitigation module's storage, the sample period to store GET
commands may easily be 10 seconds, without taxing the system.
[0094] The attack mitigation module counts the number of duplicate
GET commands that have been received and stored over the sample
period, step 404. If the number of duplicate GET commands exceeds a
threshold value, step 406, the attack mitigation module may deem an
attack to have been detected, step 408. In this embodiment, the
attack mitigation module blocks and discards any further duplicate
GET commands received from the network, step 410. A message may be
sent to a reporting system that alerts an administrator that a
GET-flood type attack may be underway, step 411. The message may be
in the form of, without limitation, an electronic mail, voice mail,
or an audio or visual alert on an administrator's computer
system.
[0095] Alternatively, if the threshold is not exceeded, the stored
GET commands are cleared from storage, step 412, and processing
moves back to step 400. In some embodiments, not all of the GET
commands are captured and stored over the sample period, but a
statistically relevant number of sampled GET commands are copied
and stored in order to save on processing time and storage.
[0096] Still, in other embodiments, in order to save storage space
and processing time, a hash, or reduction, function may be
performed on each of the GET commands, the results of which are
stored and sorted into a hash table in step 402. The hash function
may reduce each GET command to a smaller amount of data for
evaluation. If the standard deviation of the entries in the hash
table, measured in step 404, meets a threshold value, which is
checked in step 406 (for being lower in some embodiments, or higher
in other embodiments), then a network attack may be detected.
[0097] Referring to FIG. 5, a flow diagram is shown that
illustrates a method performed by one preferred embodiment of an
attack mitigation module for detecting and/or mitigating an attack
by discarding data packets that have packet headers with a suspect
user agent, or User-Agent, entry. The attack mitigation module may
be included for use in a data cleaning center protecting a
plurality of computer systems, such as that shown in FIG. 1.
Preferably, the method of FIG. 5 is executed on each of the proxy
servers (116 of FIG. 1). However, the attack mitigation module may
be used in a stand-alone device or computer system on the network
to protect one or a few server computers, and may be implemented in
software, hardware, or in a programmable logic chip, such as an
ASIC, field programmable gate array (FPGA), or the like.
[0098] In standard Internet HTTP protocol, each data packet
received has a header portion, having a user agent entry. When the
attack mitigation module receives a data packet, step 500, it reads
the user agent entry, step 502. It next determines whether the user
agent entry contains a proper value, step 504. For example, a
proper user agent header entry may resemble the following
sample:
[0099] User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT
5.0)
[0100] In most cases, an improper user agent entry is one that does
not contain an alphabetical character. Many viral or other types of
attacks on network systems send data packets that have
non-alphabetical, or sometimes blank, user agent entries.
[0101] If the entry is improper, the session from which the data
packet was sent is discarded or ended, step 506. A reporting system
may alert an administrator that there was a potential attack, step
508.
[0102] If the User-Agent value is proper, then the session is not
discarded, and if no other attack mitigation modules prevent
processing, the proxy server processes the packets in the session,
step 516.
[0103] As shown in FIG. 6, a preferred embodiment method of an
attack mitigation module that detects and/or mitigates an attack is
performed by discarding data packets that have packet headers with
suspect host value entries. Preferably, the attack mitigation
module is included for use in a data cleaning center protecting a
plurality of computer systems, such as that described in FIG. 1.
Preferably, the method of FIG. 6 is executed on each of the proxy
servers (116 of FIG. 1). However, the attack mitigation module may
be used in a stand-alone device or computer system on the network
to protect one or a few server computers, and may be implemented in
software, hardware, or in a programmable logic chip, such as an
ASIC, field programmable gate array (FPGA), or the like.
[0104] In standard Internet HTTP protocol, each data packet
received has a header portion, having a host value entry. The host
value entry is required by HTTP protocol to represent the naming
authority of the origin server or gateway given by the original
uniform resource locator (URL). This allows the origin server or
gateway to differentiate between internally-ambiguous URLs, such as
the root "/" URL of a server for multiple host names on a single IP
address.
[0105] When the attack mitigation module receives a data packet,
step 600, it reads the host value entry, step 602. It next
determines whether the host value entry contains a proper value,
step 604. For example, a proper user host value header entry may
resemble the following sample:
[0106] Host="Host" ":" host [":" port]
[0107] In most cases an improper host value entry is one that is
blank. Many viral or other types of attacks on network systems send
data packets, which have blank host value entries.
[0108] If the entry is improper, the session from which the data
packet was sent is discarded or ended, step 606. A reporting system
may alert an administrator that there was a potential attack, step
608.
[0109] If the host value entry is proper, then the session is not
discarded, and if no other attack mitigation modules prevent
processing, the proxy server processes the packets in the session,
step 616.
[0110] Referring now to FIG. 7, a flow diagram is shown that
illustrates a method performed in one exemplary embodiment of an
attack mitigation module for detecting and/or mitigating an attack
by discarding data packets that use improper end-of-line or return
characters. Preferably, the attack mitigation module is included
for use in a data cleaning center protecting a plurality of
computer systems, such as that described in FIG. 1. Preferably, the
method of FIG. 7 is executed on each of the proxy servers (116 of
FIG. 1). However, the attack mitigation module may be used in a
stand-alone device or computer system on the network to protect one
or a few server computers, and may be implemented in software,
hardware, or in a programmable logic chip, such as an ASIC, field
programmable gate array (FPGA), or the like.
[0111] In standard Internet HTTP protocol, the structures of data
packets are required to include full control-return (CR) and
linefeed (LF) characters. The standard specifically states that a
bare CR or LF should not be substituted for a full CRLF within any
of the HTTP control structures. Web browsers must send CRLF as a
line break indicator under the standard. If the session does not
use CRLF, the session is rejected.
[0112] When the attack mitigation module receives a data packet,
step 700, it reads the line break characters, step 702. It next
determines whether the line break characters are proper, step 704.
In most cases an improper line break character is one that that is
merely a CR or LF, and not a full CRLF. Many viral or other types
of attacks on network systems send data packets, which have merely
CR or LF line breaks.
[0113] If a line break is improper, the session from which the data
packet was sent is discarded or ended, step 706. A reporting system
may alert an administrator that there was a potential attack, step
708.
[0114] If the host value entry is proper, then the session is not
discarded, and if no other attack mitigation modules prevent
processing, the proxy server processes the packets in the session,
step 716.
Clean Data Redirection
[0115] Referring again to FIG. 1, with some applications of the
data cleaning center, the latency involved in using proxy servers
to proxy every data packet that is sent from a first computer (e.g.
20c) to a second computer (e.g. 80a) may slow down communications
between the first computer 20c and the second computer 80a. When
the first computer 20c and second computer 80a are physically
within the same region of the world on the Internet, the latency
involved in using the proxy servers 116, or any proxy server,
within the same region may not add very much relevant communication
time.
[0116] However, there is a unique problem that arises when, for
example, the first computer 20c and the second computer 80a are
located in the same region, for example in Australia, and the data
cleaning center 100 is located in, for example, the United States.
In this case, if the second computer 80a is a real-time processing
server, the latency period required for each packet sent between
the first computer 20c and the second computer 80a to be sent
through a proxy server 116 in the data cleaning center, or any
proxy server in the United States for that matter, could degrade
performance of time-critical or real-time applications. However,
administrators at the second computer 80a may still desire to take
advantage of the attack protection system and methods of the data
cleaning center 100.
[0117] Referring now to FIG. 8, a method is shown for preventing an
attempted overload condition targeting a networked computer system
that lessens or eliminates the latency effect of using the data
cleaning center (e.g., 100 in FIG. 1) to protect the second
computer (e.g., 80a in FIG. 1). Just as is the normal case when the
first computer (e.g. 20c in FIG. 1) requires access to the second
computer, the data cleaning center may receive one or more initial
data packets from the first computer for processing by a second
computer, step 800. For example, the one or more initial data
packets may comprise session initiating data packets so that the
first computer may initiate contract with, and set up a session for
using, the second computer.
[0118] In one embodiment, the data cleaning center redirects the
first computers to send the one or more initial data packets to a
third computer, step 802, which may comprise a proxy server (116 in
FIG. 1) within or proximate to the data cleaning center, or another
computer that may or may not be remote from the data cleaning
center. The third computer is designated to receive traffic from
the first computer until the first computer is verified not to
comprise an attacking system.
[0119] The attack mitigation modules 110 process the initial data
packets to determine whether the one or more initial data packets
are legitimate, and not a part of, for example, an attack on the
second computer, step 804. If the attack mitigation modules
determine that the initial data packets are not a part of an
attempted overload condition 110, step 806, then the first computer
is redirected to send subsequent data packets directly to the
second computer, step 808, thereby eliminating any latency that
would be associated with continuing to process subsequent data
packets in the data cleaning center.
[0120] With this embodiment and the use of the data cleaning
center, there is concern that an attack may escape detection by
delaying the attack until after the initial data packets are
processed. In order to lessen this possibility, the second computer
is configured with one or more local attack detection and/or
mitigation modules that are at the least configured to detect such
subsequent attacks, step 810. For example, a SYN-Flood mitigation
module may be installed on the second computer, or a version of the
data 100 center of FIG. 1 may be installed. If a subsequent attack
is detected, step 812, then processing of all subsequent data
packets is redirected back to the data cleaning center to use
attack mitigation modules and proxy servers to clean the data
before processing by the second computer, step 814.
[0121] In some embodiments, the domain name of the third computer
has a different prefix than the domain name of the second computer.
For example, the second computer may have a prefix of www, and the
domain name of the third computer may have a prefix of wwwn,
wherein n is a numeric value. This way, the main body of the domain
name could be the same so that users do not become confused to
think that they have been redirected to the wrong server
computer.
[0122] In one preferred embodiment, the method of the attack
mitigation module includes determining whether the initial data
packets are a part of an attack. The attack mitigation module
determines whether each received initial data packet is from a
browser executing on the first computer. For example, this can be
checked by attempting to write one or more cookies to the one or
more first computers. Viruses running on the first computer, for
example, sending data packets to the second computer currently do
not have the ability to accept cookie files from the second
computer. The failure to write the cookie file could indicate the
initial data packets are a part of the attack, and the subsequent
data packets should not be redirected to the second computer.
[0123] In another preferred embodiment, another way of determining
whether the network connection has received the initial data
packets from a browser executing on the first computer comprises
presenting text, in a distorted image, or other human only readable
test, to be typed into the one or more browsers by one or more
users. An example of a human-only readable challenge is used, by
way of example only, by Yahoo!, Inc. of Sunnyvale, Calif., in their
user-mail registration systems. Other human-only readable
challenges are also known (e.g., ticket master, and the like): If
the second computer receives an incorrect response that does not
satisfy the human-only challenge, or if there is no response at
all, as would be the case with most viruses, then an attack could
be indicated, and the subsequent data packets should not be
redirected to the second computer.
DNS Attack Mitigation
[0124] Another preferred embodiment relates to a system and method
for detecting and/or mitigating an attack targeting a domain name
service (DNS) server. The DNS server may operate remotely from the
system protecting it, as is the case with respect to one or more
second computers described in FIG. 1. A pre-processing system for
the DNS server is provided to absorb, to detect and to mitigate
attacks. However, in some configurations, the DNS server may use
its own protection system embodied in a separate processor
connected between the network and the DNS server, or in a local
processor embedded within the DNS server itself.
[0125] FIG. 9 illustrates an embodiment of the DNS server
protection system 900 to protect a DNS server 30. A network
connection 126 is provided for receiving one or more DNS requests
from one or more client computers 22a, 22b and 22c located on the
network 10. A preferred embodiment includes a processor 902,
separate from that normally used by the DNS server 30, for
providing a response for the one or more DNS requests to the one or
more client computers 22a, 22b and 22c before or instead of normal
processing by the DNS server 30.
[0126] In one embodiment, the processor 902 protects two or more
load balanced DNS servers 30. A load balancing router 950 performs
load balancing between the DNS servers 30.
[0127] Preferably, the added processor 902 monitors the volume of
requests received per second to the DNS servers 30. If a threshold
volume is detected, then processing of the DNS requests is diverted
to the processor 902.
[0128] Referring now to FIG. 10, a flow diagram is shown that
illustrates a preferred method preformed by the DNS protection
system for detecting and/or mitigating an attack targeting the DNS
server. One or more DNS requests are received from the one or more
client computers located on a network, step 1000. The processor 902
checks for whether the request is directed to port 53, step 1002.
All requests not directed to part 53 are discarded, step 1004. A
sanity check is performed on the request, which determines whether
DNS standard request requirements are met in the request, step
1006. Standards for DNS requirements may be found by contacting the
Internet Engineering. Task Force (www.IETF.org). Specifically,
standards may be viewed in the request for comments (RFC) section
of the IETF web site. If the request does not comply with DNS
requirements, the request is discarded, step 1004.
[0129] Next, the processor 902 determines whether the request is
for a domain name on a list of valid domain names for the DNS
server, step 1008. If not, then the request is discarded, step
1004.
[0130] If the request is not discarded, the processor 902 places
the request in a database, step 1010. The database may be keyed by
the source address, and target domain name requested. Further, a
hit count is kept in the database to count the number of
(duplicate) requests for each source address and request.
[0131] The processor 902 checks for whether the recorded hit count
for the request exceeds a threshold for the number of requests over
a period of time (for example, over the last ten seconds), step
1212. The threshold is based on the capacity of the DNS sever(s)
30. If the threshold is exceeded, then the processor 902 itself
services all requests for the particular source address and target
domain requested until the hit count is reduced, step 1014. If
necessary, the processor 902 makes a request to the DNS server 30
to obtain the IP address to answer the request. However, in one
embodiment, the required information is kept in a memory in the DNS
protection system 900.
[0132] Otherwise, if the hit count threshold is not exceeded, the
DNS sever(s) 30 process the request directly, step 1016.
[0133] Referring again to FIG. 9, the processor 902 is preferably
configured to execute instructions as fast as possible, given the
size and speed of attacks that typically are to be handled by the
processor. Thus, in a preferred embodiment, the instructions to
respond to requests are built directly into the chip logic of the
processor 902. The list of valid domain names may be stored in a
database 912 in a high-speed memory 920 in the DNS protection
system 900. The high-speed memory 920 is preferably connected to
the processor 902 through a high-speed data bus 922 Further, the
database of received requests and hit counts are stored in a sorted
database 914 located in the high-speed memory 920.
[0134] A cache 916 of requests previously processed by the DNS
server 30 may be stored in the memory 920 so that the processor 902
may perform step 1014 of FIG. 10 without the need to make a special
request to the DNS server(s) 30.
[0135] It will be apparent from the foregoing that, while
particular forms of the invention have been illustrated and
described, various modifications can be made without departing from
the spirit and scope of the invention. Accordingly, it is not
intended that the invention be limited, except as by the appended
claims.
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