Method and computer readable medium for suppressing execution of signature file directives during a network exploit

Abstract

A method of analyzing packets at a node of a network by an intrusion prevention system executed by the node, comprising reading the packet by the intrusion prevention system, comparing the packet with a machine-readable signature file, determining the packet has a packet signature that corresponds with the machine-readable signature file, and determining the machine-readable signature file has an associated squelch comprising a squelch threshold and a squelch period is provided. A computer-readable medium having stored thereon a set of instructions to be executed, the set of instructions that, when executed by a processor, cause the processor to perform a computer method of reading a packet, comparing the packet with a machine-readable signature file, determining the packet has a packet signature that corresponds with the machine-readable signature file, and determining the machine-readable signature file has an associated squelch comprising a squelch threshold and a squelch period is provided.

Description

TECHNICAL FIELD OF THE INVENTION

[0002] This invention relates to network technologies and, more particularly, to method and computer readable medium for suppressing execution of directives of a signature file during a network exploit.

BACKGROUND OF THE INVENTION

[0003] Network-exploit attack tools, such as denial-of-service (DoS) attack utilities, are becoming increasing sophisticated and, due to evolving technologies, simple to execute. Relatively unsophisticated attackers can arrange, or be involved in, computer system compromises directed at one or more targeted facilities. A network system attack (also referred to herein as an intrusion) is an unauthorized or malicious use of a computer or computer network and may involve hundreds or thousands of unprotected, or alternatively compromised, Internet nodes together in a coordinated attack on one or more selected targets.

[0004] Network attack tools based on the client/server model have become a preferred mechanism for executing network attacks on targeted networks or devices. High capacity machines in networks having deficient security are often desired by attackers to launch distributed attacks therefrom. University servers typically feature high connectivity and capacity but relatively mediocre security. Such networks also often have inexperienced or overworked network administrators making them even more vulnerable for involvement in network attacks.

[0005] Network-exploit attack tools, comprising hostile attack applications such as denial-of-service (DoS) utilities, responsible for transmitting data across a network medium will often have a distinctive “signature,” or recognizable pattern within the transmitted data. The signature may comprise a recognizable sequence of particular packets and/or recognizable data that is contained within one or more packets. Signature analysis is often performed by a network intrusion prevention system (IPS) and may be implemented as a pattern-matching algorithm and may comprise other signature recognition capabilities as well as higher-level application monitoring utilities. A simple signature analysis algorithm may search for a particular string that has been identified as associated with a hostile application. Once the string is identified within a network data stream, the one or more packets carrying the string may be identified as “hostile,” or exploitative, and the IPS may then perform any one or more of a number of actions, such as logging the identification of the frame, performing a countermeasure, or performing another data archiving or protection measure.

[0006] Intrusion prevention systems (IPS) encompass technology that attempts to identify exploits against a computer system or network of computer systems. Numerous types of IPSs exist and each are generally classified as either a network-based, host-based, or node-based IPS.

[0007] Network-based IPS appliances are typically dedicated systems placed at strategic places on a network to examine data packets to determine if they coincide with known attack signatures. To compare packets with known attack signatures, network-based IPS appliances utilize a mechanism referred to as passive protocol analysis to inconspicuously monitor, or “sniff,” all traffic on a network and to detect low-level events that may be discerned from raw network traffic. Network exploits may be detected by identifying patterns or other observable characteristics of network frames. Network-based IPS appliances examine the contents of data packets by parsing network frames and packets and analyzing individual packets based on the protocols used on the network. A network-based IPS appliance inconspicuously monitors network traffic inconspicuously, i.e., other network nodes may be, and often are, unaware of the presence of the network-based IPS appliance. Passive monitoring is normally performed by a network-based IPS appliance by implementation of a “promiscuous mode” access of a network interface device. A network interface device operating in promiscuous mode copies packets directly from the network media, such as a coaxial cable, 100baseT or other transmission medium, regardless of the destination node to which the packet is addressed. Accordingly, there is no simple method for transmitting data across the network transmission medium without the network-based IPS appliance examining it and thus the network-based IPS appliance may capture and analyze all network traffic to which it is exposed. Upon identification of a suspicious packet, i.e., a packet that has attributes corresponding to a known attack signature monitored for occurrence by the network-based IPS appliance, an alert may be generated thereby and transmitted to a management module of the IPS so that a networking expert may implement security measures. Network-based IPS appliances have the additional advantage of operating in real-time and thus can detect an attack as it is occurring. Moreover, a network-based IPS appliance is ideal for implementation of a state-based IPS security measure that requires accumulation and storage of identified suspicious packets of attacks that may not be identified “atomically,” that is by a single network packet. For example, transmission control protocol (TCP) synchronization (SYN) flood attacks are not identifiable by a single TCP SYN packet but rather are generally identified by accumulating a count of TCP SYN packets that exceed a predefined threshold over a defined period of time. A network-based IPS appliance is therefore an ideal platform for implementing state-based signature detection because the network-based IPS appliance may collect all such TCP SYN packets that pass over the local network media and thus may properly archive and analyze the frequency of such events.

[0008] However, network-based IPS appliances may often generate a large number of “false positives,” i.e., incorrect diagnoses of an attack. False positive diagnoses by network-based IPS appliances result, in part, due to errors generated during passive analysis of all the network traffic captured by the IPS that may be encrypted and formatted in any number of network supported protocols. Content scanning by a network-based IPS is not possible on an encrypted link although signature analysis based on protocol headers may be performed regardless of whether the link is encrypted or not. Additionally, network-based IPS appliances are often ineffective in high speed networks. As high speed networks become more commonplace, software-based network-based IPS appliances that attempt to sniff all packets on a link will become less reliable. Most critically, network-based IPS appliances can not prevent attacks unless integrated with, and operated in conjunction with, a firewall protection system.

[0009] Host-based IPSs detect intrusions by monitoring application layer data. Host-based IPSs employ intelligent agents to continuously review computer audit logs for suspicious activity and compare each change in the logs to a library of attack signatures or user profiles. Host-based IPSs may also poll key system files and executable files for unexpected changes. Host-based IPSs are referred to as such because the IPS utilities reside on the system to which they are assigned to protect. Host-based IPSs typically employ application-level monitoring techniques that examine application logs maintained by various applications. For example, a host-based IPS may monitor a database engine that logs failed access attempts and/or modifications to system configurations. Alerts may be provided to a management node upon identification of events read from the database log that have been identified as suspicious. Host-based IPSs, in general, generate very few false-positives. However, host-based IPS such as log-watchers are generally limited to identifying intrusions that have already taken place and are also limited to events occurring on the single host. Because log-watchers rely on monitoring of application logs, any damage resulting from the logged attack will generally have taken place by the time the attack has been identified by the IPS. Some host-based IPSs may perform intrusion-preventative functions such as ‘hooking’ or ‘intercepting’ operating system application programming interfaces to facilitate execution of preventative operations by an IPS based on application layer activity that appears to be intrusion-related. Because an intrusion detected in this manner has already bypassed any lower level IPS, a host-based IPS represents a last layer of defense against network exploits. However, host-based IPSs are of little use for detecting low-level network events such as protocol events.

[0010] Node-based IPSs apply the intrusion detection and/or prevention technology on the system being protected. An example of node-based IPS technologies is inline intrusion detection. A node-based IPS may be implemented at each node of the network that is desired to be protected. Inline IPSs comprise intrusion detection technologies embedded in the protocol stack of the protected network node. Because the inline IPS is embedded within the protocol stack, both inbound and outbound data will pass through, and be subject to monitoring by, the inline IPS. An inline IPS overcomes many of the inherent weaknesses of network-based solutions. As mentioned hereinabove, network-based solutions are generally ineffective when monitoring high-speed networks due to the fact that network-based solutions attempt to monitor all network traffic on a given link. Inline intrusion prevention systems, however, only monitor traffic directed to the node on which the inline IPS is installed. Thus, attack packets can not physically bypass an inline IPS on a targeted machine because the packet must pass through the protocol stack of the targeted device. Any bypassing of an inline IPS by an attack packet must be done entirely by ‘logically’ bypassing the IPS, i.e., an attack packet that evades an inline IPS must do so in a manner that causes the inline IPS to fail to identify, or improperly identify, the attack packet. Additionally, inline IPSs provide the hosting node with low-level monitoring and detection capabilities similar to that of a network IPS and may provide protocol analysis and signature matching or other low-level monitoring or filtering of host traffic. The most significant advantage offered by inline IPS technologies is that attacks are detected as they occur. Whereas host-based IPSs determine attacks by monitoring system logs, inline intrusion detection involves monitoring network traffic and isolating those packets that are determined to be part of an attack against the hosting server and thus enabling the inline IPS to actually prevent the attack from succeeding. When a packet is determine to be part of an attack, the inline IPS layer may discard the packet thus preventing the packet from reaching the upper layer of the protocol stack where damage may be caused by the attack packet—an effect that essentially creates a local firewall for the server hosting the inline IPS and protecting it from threats coming either from an external network, such as the Internet, or from within the network. Furthermore, the inline IPS layer may be embedded within the protocol stack at a layer where packets have been unencrypted so that the inline IPS is effective operating on a network with encrypted links. Additionally, inline IPSs can monitor outgoing traffic because both inbound and outbound traffic respectively destined to and originating from a server hosting the inline IPS must pass through the protocol stack.

[0011] Although the advantages of inline IPS technologies are numerous, there are drawbacks to implementing such a system. Inline intrusion detection is generally processor intensive and may adversely effect the node's performance hosting the detection utility. Additionally, inline IPSs may generate numerous false positive attack diagnoses. Furthermore, inline IPSs cannot detect systematic probing of a network, such as performed by reconnaissance attack utilities, because only traffic at the local server hosting the inline IPS is monitored thereby.

[0012] Each of network-based, host-based and inline-based IPS technologies have respective advantages as described above. Ideally, an intrusion prevention system will incorporate all of the aforementioned intrusion detection strategies. Additionally, an IPS may comprise one or more event generation mechanisms that report identifiable events to one or more management facilities. An event may comprise an identifiable series of system or network conditions or it may comprise a single identified condition. An IPS may also comprise an analysis mechanism or module and may analyze events generated by the one or more event generation mechanisms. A storage module may be included within an IPS for storing data associated with intrusion-related events. A countermeasure mechanism may also be included within the IPS for executing an action intended to thwart, or negate, a detected exploit.

[0013] Typical IPSs are particularly vulnerable to bandwidth-consumption type exploits such as distributed denial of service attacks. These exploits flood the targeted system in an effort to consume all available resources and cripple the operating system and/or the IPS. Typical bandwidth consumption attacks take the form of a distributed coordinated attack from many machines that direct the attack at a single targeted node. Even an IPS that may recognize the attack is often unable to defend the targeted system against such an attack as the attacker can simply increase the number of systems included in the distributed attack until the amount of processing required by the targeted system for managing intrusion-related event processing overwhelms the node.

SUMMARY OF THE INVENTION

[0014] In accordance with an embodiment of the present invention, a method of analyzing frames at a node of a network by an intrusion prevention system executed by the node comprising reading a frame by the intrusion prevention system, comparing the frame with a machine-readable signature file, determining the frame has a frame signature that corresponds with the machine-readable signature file, and determining the machine-readable signature file has an associated squelch comprising a squelch threshold and a squelch period is provided.

[0015] In accordance with another embodiment of the present invention, a computerreadable medium having stored thereon a set of instructions to be executed, the set of instructions that, when executed by a processor, cause the processor to perform a computer method of reading a frame, comparing the frame with a machine-readable signature file, determining the frame has a frame signature that corresponds with the machine-readable signature file, and determining the machine-readable signature file has an associated squelch comprising a squelch threshold and a squelch period is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a more complete understanding of the present invention, the objects and advantages thereof, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

[0017] FIG. 1 illustrates an exemplary arrangement for executing a computer system compromise according to the prior art;

[0018] FIG. 2 illustrates a comprehensive intrusion prevention system employing network-based and hybrid host-based and node based intrusion detection technologies according to an embodiment of the invention;

[0019] FIG. 3 is an exemplary network protocol stack according to the prior art;

[0020] FIG. 4 illustrates a network node that may run an instance of an intrusion protection system application according to an embodiment of the present invention;

[0021] FIG. 5 illustrates an exemplary network node that may operate as a management node within a network protected by the intrusion protection system according to an embodiment of the present invention;

[0022] FIG. 6 illustrates an exemplary protocol stack having an intrusion prevention system inserted therein and in which a signature analysis process according to an embodiment of the present invention may be employed; and

[0023] FIG. 7 is a flowchart of a signature analysis procedure according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0024] The preferred embodiment of the present invention and its advantages are best understood by referring to FIGS. 1 through 7 of the drawings, like numerals being used for like and corresponding parts of the various drawings.

[0025] In FIG. 1, there is illustrated an exemplary arrangement for executing a computer system compromise—the illustrated example showing a simplified distributed intrusion network 40 arrangement typical of distributed system attacks directed at a target machine 30. An attack machine 10 may direct execution of a distributed attack by any number of attacker attack agents 20A-20N by one of numerous techniques such as remote control by IRC “robot” applications. Attack agents 20A-20N, also referred to as “zombies” and “attack agents,” are generally computers that are available for public use or that have been compromised such that a distributed attack may be launched upon command of an attack machine 10. Numerous types of distributed attacks may be launched against a target machine 30. The target machine 30 may suffer extensive damage from simultaneous attack by attack agents 20A-20N and the attack agents 20A-20N may be damaged from the client attack application as well. A distributed intrusion network may comprise an additional layer of machines involved in an attack intermediate the attack machine 10 and attack agents 20A-20N. These intermediate machines are commonly referred to as “handlers” and each handler may control one or more attack agents 20A-20N. The arrangement shown for executing a computer system compromise is illustrative only and may compromise numerous arrangements that are as simple as a single attack machine 10 attacking a target machine 30 by, for example, sending malicious probe packets or other data intended to compromise target machine 30. Target machine may be, and often is, connected to a larger network and access thereto by attack machine 10 may cause damage to a large collection of computer systems commonly located within the network.

[0026] In FIG. 2, there is illustrated a comprehensive intrusion prevention system employing network-based and hybrid host-based/node-based intrusion detection technologies according to an embodiment of the invention. One or more networks 100 may interface with the Internet 50 via a router 45 or other device. In the illustrative example, network 100 comprises two Ethernet networks 55 and 56. Ethernet network 55 comprises a web-content server 270A and a file transport protocol-content server 270B. Ethernet network 56 comprises a domain name server 270C, a mail server 270D, a database sever 270E and a file server 270F. A firewall/proxy router 60 disposed intermediate Ethernets 55 and 56 provides security and address resolution to the various systems of network 56. A network-based IPS appliance 80 and 81 is respectively implemented on both sides of firewall/proxy router 60 to facilitate monitoring of attempted attacks against one or more elements of Ethernets 55 and 56 and to facilitate recording successful attacks that successfully penetrate firewall/proxy router 60. Network-based IPS appliances 80 and 81 may respectively comprise (or alternatively be connected to) a database 80A and 81A of known attack signatures, or rules, against which network frames captured thereby may be compared. Alternatively, a single database (not shown) may be centrally located within network 100 and may be accessed by network-based IPS appliances 80 and 81. Accordingly, network-based IPS appliance 80 may monitor all packets inbound from Internet 50 to network 100 arriving at Ethernet network 55. Similarly, a network-based IPS appliance 81 may monitor and compare all packets passed by firewall/proxy router 60 for delivery to Ethernet network 56. An IPS management node 85 may also be part of network 100 to facilitate configuration and management of the IPS components in network 100.

[0027] In view of the above-noted deficiencies of network-based intrusion prevention systems, a hybrid host-based and node-based intrusion prevention system is preferably implemented within each of the various nodes, such as servers 270A-270N (also referred to herein as “nodes”), of Ethernet networks 55 and 56 in the secured network 100. Management node 85 may receive alerts from respective nodes within network 100 upon detection of an intrusion event by any one of the network-based IPS appliances 80 and 81 as well as any of the nodes of network 100 having a hybrid agent-based and node-based IPS implemented thereon. Additionally, each node 270A-270F may respectively employ a local file system for archiving intrusion-related events, generating intrusion-related reports, and storing signature files against which local network frames and/or packets are examined.

[0028] Preferably, network-based IPS appliances 80 and 81 are dedicated entities for monitoring network traffic on associated Ethernets 55 and 56 of network 100. To facilitate intrusion detection in high speed networks, network-based IPS appliances 80 and 81 preferably comprise a large capture RAM for capturing packets as they arrive on respective Ethernet networks 55 and 56. Additionally, it is preferable that network-based IPS appliances 80 and 81 respectively comprise hardware-based filters for filtering network traffic, although IPS filtering by network-based IPS appliances 80 and 81 may be implemented in software. Moreover, network-based IPS appliances 80 and 81 may be configured, for example by demand of IPS management node 85, to monitor one or more specific devices rather than all devices on a common network. For example, network-based IPS appliance 80 may be directed to monitor only network data traffic addressed to web server 270A.

[0029] Hybrid host-based/node-based intrusion prevention system technologies may be implemented on all nodes 270A-270N on Ethernet networks 55 and 56 that may be targeted by a network attack. In general, each node is comprised of a reprogrammable computer having a central processing unit (CPU), a memory module operable to store machine-readable code that is retrievable and executable by the CPU, and may further comprise various peripheral devices, such as a display monitor, a keyboard, a mouse or another device, connected thereto. A storage media, such as a magnetic disc, an optical disc or another component operable to store data, may be connected to memory module and accessible thereby and may provide one or more databases for archiving local intrusion events and intrusion event reports. An operating system may be loaded into memory module, for example upon bootup of the respective node, and comprises an instance of a protocol stack as well as various low-level software modules required for tasks such as interfacing to peripheral hardware, scheduling of tasks, allocation of storage as well as other system tasks. Each node protected by the hybrid host-based and node-based IPS of the present invention accordingly has an IPS software application maintained within the node, such as in a magnetic hard disc, that is retrievable by the operating system and executable by the central processing unit. Additionally, each node executing an instance of the IPS application has a local database from which signature descriptions of documented attacks may be fetched from storage and compared with a packet or frame of data to detect a correspondence therebetween. Detection of a correspondence between a packet or frame at an IDS server may result in execution of any one or more of various security procedures.

[0030] The IPS described with reference to FIG. 2 may be implemented on any number of platforms. Each hybrid host-based/node-based instance of the IPS application described herein is preferably implemented on a network node, such as web server 270A operated under control of an operating system, such as Windows NT 4.0 that is stored in a main memory and running on a central processing unit, and attempts to detect attacks targeted at the hosting node. The particular network 100 illustrated in FIG. 2 is exemplary only and may comprise any number of network nodes, such as network servers or computers. Corporate, and other large scale, networks may typically comprise numerous individual systems providing similar services. For example, a corporate network may comprise hundreds of individual web servers, mail servers, FTP servers and other systems providing common data services.

[0031] Each operating system of a node incorporating an instance of an IPS application additionally comprises a network protocol stack 90, as illustrated in FIG. 3, that defines the entry point for frames received by a targeted node from the network, e.g. the Internet or Intranet. Network stack 90 as illustrated is representative of the well-known WindowsNT (TM) system network protocol stack and is so chosen to facilitate discussion and understanding of the invention. However, it should be understood that the invention is not limited to a specific implementation of the illustrated network stack 90 but, rather, stack 90 is described to facilitate understanding of the invention. Network stack 90 comprises a transport driver interface (TDI) 125, a transport driver 130, a protocol driver 135 and a media access control (MAC) driver 145 that interfaces with the physical media 101. Transport driver interface 125 functions to interface the transport driver 130 with higher-level file system drivers. Accordingly, TDI 125 enables operating system drivers, such as network redirectors, to activate a session, or bind, with the appropriate protocol driver 135. Accordingly, a redirector can access the appropriate protocol, for example UDP, TCP, NetBEUI or other network or transport layer protocol, thereby making the redirector protocol-independent. The protocol driver 135 creates data packets that are sent from the computer hosting the network protocol stack 90 to another computer or device on the network or another network via the physical media 101. Typical protocols supported by an NT network protocol stack comprise NetBEUI, TCP/IP, NWLink, Data Link Control (DLC) and AppleTalk although other transport and/or network protocols may be supported. MAC driver 145, for example an Ethernet driver, a token ring driver or other networking driver, provides appropriate formatting and interfacing with the physical media 101 such as a coaxial cable or another transmission medium.

[0032] The capabilities of the host-based IPS comprise application monitoring of: file system events; registry access; successful security events; failed security events and suspicious process monitoring. Network access applications, such as Microsoft IIS and SQL Server, may also have processes related thereto monitored.

[0033] Intrusions may be prevented on a particular IPS host by implementation of inline, node-based monitoring technologies. The inline-IPS is preferably included as part of a hybrid host-based/node-based IPS although it may be implemented independently of any host-based IPS system. The inline-IPS will analyze packets received at the hosting node and perform signature analysis thereof against a database of known signatures by network layer filtering.

[0034] In FIG. 4, there is illustrated a network node 270 that may run an instance of an IPS application 91 and thus operate as an IPS server. IPS application 91 may be implemented as a three-layered IPS, as described in co-pending application entitled “Method, Computer Readable Medium, and Node for a Three-Layered Intrusion Prevention System for Detecting Network Exploits” and filed concurrently herewith, and may comprise a server application and/or a client application. Network node 270, in general, comprises a central processing unit (CPU) 272 and a memory module 274 operable to store machine-readable code that is retrievable and executable by CPU 272 via a bus (not shown). A storage media 276, such as a magnetic disc, an optical disc or another component operable to store data, may be connected to memory module 274 and accessible thereby by the bus as well. An operating system 275 may be loaded into memory module 274, for example upon bootup of node 270, and comprises an instance of protocol stack 90 and may have an intrusion prevention system application 91 loaded from storage media 276. One or more network exploit rules, an exemplary form described in co-pending application entitled “Method, Node and Computer Readable Medium for Identifying Data in a Network Exploit” and filed concurrently herewith, may be compiled into a machine-readable signature(s) and stored within a database 277 that is loadable into memory module 274 and may be retrieved by IPS application 91 for facilitating analysis of network frames and/or packets.

[0035] In FIG. 5, there is illustrated an exemplary network node that may operate as a management node 85 of the IPS of a network 100. Management node 85, in general, comprises a CPU 272 and a memory module 274 operable to store machine-readable code that is retrievable and executable by CPU 272 via a bus (not shown). A storage media 276, such as a magnetic disc, an optical disc or another component operable to store data, may be connected to memory module 274 and accessible thereby by the bus as well. An operating system 275 may be loaded into memory module 274, for example upon bootup of node 85, and comprises an instance of protocol stack 90. Operating system 275 is operable to fetch an IPS management application 279 from storage media 276 and load management application 279 into memory module 274 where it may be executed by CPU 272. Node 85 preferably has an input device 281, such as a keyboard, and an output device 282, such as a monitor, connected thereto.

[0036] An operator of management node 85 may input one or more text-files 277A-277N via input device 281. Each text-file 277A-277N may defme a network-based exploit and comprise a logical description of an attack signature as well as IPS directives to execute upon an IPS evaluation of an intrusion-related event associated with the described attack signature. Each text file 277A-277N may be stored in a database 278A on storage media 276 and compiled by a compiler 280 into a respective machine-readable signature file 281A-281N that is stored in a database 278B. Each of the machine-readable signature files 281A-281N comprises binary logic representative of the attack signature as described in the respectively associated text-file 277A-277N. An operator of management node 85 may periodically direct management node 85, through interaction with a client application of IPS application 279 via input device 281, to transmit one or more machine-readable signature files (also generally referred to herein as “signature files”) stored in database 278B to a node, or a plurality of nodes, in network 100. Alternatively, signature files 281A-281N may be stored on a computer-readable medium, such as a compact disk, magnetic floppy disk or another portable storage device, and installed on node 270 of network 100. Application 279 is preferably operable to transmit all such signature-files 281A-281N, or one or more subsets thereof, to a node, or a plurality of nodes, in network 100. Preferably, IPS application 279 provides a graphical user interface on output device 282 for facilitating input of commands thereto by an operator of node 85.

[0037] In FIG. 6, there is illustrated an exemplary protocol stack 90A having an intrusion protection system inserted therein and in which a signature analysis process of the present invention may be employed. Network stack 90A comprises TDI 125, a transport driver 130, a protocol driver 135 and a media access control (MAC) driver 145 that interfaces with the physical media 101. Transport driver interface 125 finctions to interface the transport driver 130 with higher-level file system drivers and enables operating system drivers to bind with an appropriate protocol driver 135. Protocol driver 135 creates data packets that are sent from the computer hosting network protocol stack 90A to another computer or device on the network or another network via physical media 101. MAC driver 145 provides appropriate formatting and interfacing with the physical media 101. Network stack 90A additionally may comprise a dynamically linked library 115 that allows a plurality of subroutines to be accessed by applications 105, comprising an IPS server, at application layer 112 of network stack 90A and facilitates linking with other applications thereby. Dynamically linked library 115 may alternatively be omitted and the functionality thereof may be incorporated into the operating system kernel as is understood in the art.

[0038] An intrusion prevention system network filter service provider 140 is installed above the physical media driver 145, such as an Ethernet driver, token ring driver, etc., and bound thereto. Intrusion prevention system network filter service provider 140 is preferably bound to protocol driver 135 as well. Thus, all machine-readable signature files maintained in database 277 may thereby be validated against incoming and outgoing frames. IPS network filter service provider 140 provides low level-filtering to facilitate suppression of network attacks comprising, but not limited to, “atomic” network attacks, network protocol level attacks, IP port filtering, and also serves to facilitate collection of network statistics. Accordingly, by implementing a filter service provider 140 of the IPS at the network layer of network stack 90A, the IPS observes identical data that the network stack processes and is able to suppress inbound and/or outbound data at the network layer. Accordingly, filter service provider 140 may evaluate execution of IPS services based on processing behavior of the network stack.

[0039] A common attack technique for circumventing an IPS involves intentionally launching a series of attack packets at a node that each violate a signature file thereof in order to cause the IPS to generate a series of intrusion-report frames or to cause the IPS to execute any number of processor-intensive countermeasures such that the IPS may become overloaded and disabled—an attack technique commonly referred to as a bandwidth consumption attack. For example, as an IPS network filter service provider 140 detects an intrusion-related event, for example a correspondence between a network frame analyzed thereby and a signature file, such as one or more signature files 281A-281N stored in database 277, a report frame may be generated by IPS network filter service provider 140 and passed to an IPS server running at application layer 112 where it may be analyzed, archived, used in generation of an intrusion report, used to trigger a countermeasure or to activate another security measure. Generation of a report frame, and subsequent processes resulting therefrom, consume processor resources at the node running the IPS. IPS applications of the prior art will generate a report and transmit the report to management node 85 or to a local archive each instance a network-exploit rule is violated in prior art IPSs. As described, an attacker is often able to take advantage of the report generation mechanisms implemented to facilitate disablement of a prior art IPS. The attacker may then commence any number of attacks on the targeted node.

[0040] According to the present invention, signature files generated from network exploit rules may be analyzed in real-time and are configured with a suppression count and suppression interval to avoid the overhead of logging network-exploit events when the system is being rapidly attacked and system resources are limited. FIG. 7 shows a flowchart of a signature analysis procedure according to an embodiment of the invention. A squelch routine may be implemented in IPS application 91. The squelch routine processing illustrated by the flowchart of FIG. 7 facilitates a reduction of false-positive reports and exploit-event report generation that may otherwise be used to disable an IPS in a bandwidth-consumption exploit. As described hereinabove, one or more IPS directives may be included in a given signature file that logically defines an action the IPS is to perform upon detection of an intrusion event related to the signature file. A squelch is preferably defined in a signature file and comprises a squelch period and a squelch threshold. A frame counter is maintained by the node running the signature analysis process of the invention and may be incremented each time a signature rule is violated, that is each time an analyzed frame or packet is detected as having a signature corresponding to a machine-readable signature file 281A-281N. Event logging and other management procedures or directives defined in the signature file, such as generation of exploit-event reports by the targeted node and transmission of the exploit-event reports to management node 85, that are to be performed by the IPS upon detection of an intrusion-event, or signature violation, may be suspended when the frame counter exceeds a specified squelch threshold during a predefined time interval or squelch period. The squelch may be generically designated such that violation of any rule of all signatures recognizable by the IPS results in an increment of the frame counter. Alternatively, each signature file may have an individually designated squelch threshold and squelch period assigned thereto.

[0041] While the signature analysis process of FIG. 7 is described with reference to frame signature analysis, it is understood that packet signature analysis may be substituted therefor. The signature analysis process of the invention begins when a frame is read by the IPS (step 151). A signature file may be processed by the IPS and an evaluation of whether the signature file is enabled is made (step 152). If the signature file is disabled, an exemplary technique thereof described in co-pending application entitled “Node, Method and Computer Readable Medium for Optimizing Performance of Signature Rule Matching in a Network” and filed concurrently herewith, the signature analysis process returns to await reading of the next frame. Upon evaluation that the signature file is enabled, a determination of violation of the signature file is made, i.e., an evaluation of a correspondence between the frame read and a signature file is performed by, for example, a pattern matching algorithm or another signature comparison technique (step 153). Upon confirmation that an active signature file has been violated, an analysis of the signature file is made to determine whether the signature file has an enabled squelch associated therewith (step 154). Evaluation of a non-enabled squelch results in execution of the directives of the signature file (step 155) and the signature analysis process returns to await reading of the next frame. An affirmative evaluation of an enabled squelch of an active signature file results in analysis of the defined squelch period to determine whether the squelch period has elapsed (step 156). A new squelch period is initiated if the squelch period has elapsed since the previous identification of a frame identified as matching the signature file (step 158). However, if the squelch period has not elapsed, an analysis is made to determine whether the squelch threshold has been exceeded by the frame counter that increments each time a given signature file is violated by an analyzed signature of a read frame. The signature file directive(s) is executed in the event the squelch threshold has not been exceeded by the frame counter (step 155). Confirmation of an exceeded squelch threshold results in suppression, that is rejection, of execution of one or more signature file directives such as transmission of an exploit-report frame and/or rejection of another processor-intensive security measures such as logging of the exploit frame (step 159) such that a reduction in the amount of intrusion-related event logging is achieved without compromising the security policies of IPS 91, that is IPS 91 may continue to filter for intrusion-related packets and/or frames while reducing processor overhead that would otherwise be required by execution of directives such as logging of intrusion-related data. The frame counter is incremented (step 160) in either case that the squelch period has elapsed or not (step 160) in order to record the occurrence of the correspondence between the read frame and the signature file. The signature analysis routine then evaluates whether more signature files remain (step 162), such as in database 277, for comparison with the read frame, and the process is returned, upon an affirmative evaluation, to determine whether the remaining signature files are active (step 152). If no signature files remain for comparison with the read frame, the process returns to wait for reading of the next frame. Accordingly, once the suppression count has been reached, exploit reports, or execution of other signature file directives, generated by the attacked node may be suppressed so that an overflow of event notifications is prevented from consuming system resources.

[0042] The signature analysis process described may be implemented in machine-readable code and may be executed by any node of network 100 having a processor operable to read and execute the machine-readable code. The machine-readable code comprising logic for causing the signature analysis process to be performed by a processor may be delivered electronically thereto or may be carried on a computer readable medium such as magnetic disc, optical disc or another medium suitable for storage and delivery of machine-readable instruction sets.

Claims

1. A method of analyzing frames at a node of a network by an intrusion prevention system executed by the node, comprising: reading the frame by the intrusion prevention system; comparing the frame with a machine-readable signature file; determining the frame has a frame signature that corresponds with the machine-readable signature file; and determining the machine-readable signature file has an associated squelch comprising a squelch threshold and a squelch period.

2. The method according to claim 1, further comprising disabling execution of a directive of the machine-readable signature file if a frame counter exceeds the squelch threshold.

3. The method according to claim 1, further comprising incrementing a frame counter upon determination that the frame signature corresponds with the machine-readable signature.

4. The method according to claim 1, further comprising determining whether the squelch period has elapsed.

5. The method according to claim 4, further comprising initiating a new squelch period upon determining the squelch period has elapsed.

6. The method according to claim 3, further comprising determining if the squelch threshold has been exceed by the frame counter.

7. The method according to claim 1, further comprising executing a directive of the machine-readable signature file upon determination that the squelch threshold has not been exceeded.

8. The method according to claim 1, further comprising suppressing execution of a directive of the signature file upon determination that the squelch threshold has been exceeded.

9. The method according to claim 8, wherein suppressing execution of a directive of the signature file further comprises suppressing execution of report generation associated with the determination that the frame signature corresponds with the machine-readable signature file.

10. A computer-readable medium having stored thereon a set of instructions to be executed, the set of instructions, when executed by a processor, cause the processor to perform a computer method of: reading a frame; comparing the frame with a machine-readable signature file; determining the frame has a frame signature that corresponds with the machine-readable signature file; and determining the machine-readable signature file has an associated squelch comprising a squelch threshold and a squelch period.

11. The computer readable medium according to claim 10, further comprising a set of instruction that, when executed by the processor, cause the processor to perform a computer method of periodically incrementing a squelch period timer assigned to the machine-readable signature file.

12. The computer readable medium according to claim 11, further comprising a set of instructions that, when executed by the processor, cause the processor to perform a computer method of determining if the squelch period timer equals or exceed the squelch period.

13. The computer readable medium according to claim 12, further comprising a set of instructions that, when executed by the processor, cause the processor to perform a computer method of: re-initiating the squelch period timer upon determination that the squelch period timer equals or exceeds the squelch period; and incrementing a frame counter upon determining the frame signature corresponds with the machine-readable signature file.

14. The computer readable medium according to claim 12, further comprising a set of instructions that, when executed by the processor, cause the processor to perform a computer method of determining if a frame counter exceeds the squelch threshold.

15. The computer readable medium according to claim 14, further comprising a set of instructions that, when executed by the processor, cause the processor to perform a computer method of suppressing execution of a directive of the signature file upon determination that the squelch threshold has been exceeded by the frame counter.

16. The computer readable medium according to claim 14, further comprising a set of instructions that, when executed by the processor, cause the processor to perform a computer method of executing a directive of the signature file upon determination that the squelch threshold has not been exceeded by the frame counter.

17. The computer readable medium according to claim 15, wherein suppressing execution of a directive further comprises suppressing execution of a report generation associated with the determination that the frame signature corresponds with the machine-readable signature file.

18. The computer readable medium according to claim 13, further comprising a set of instructions that, when executed by the processor, cause the processor to perform a computer method of determining if the squelch is enabled.

19. The computer readable medium according to claim 13, further comprising a set of instructions that, when executed by the processor, cause the processor to perform a computer method of executing a directive of the signature file upon determining the squelch is disabled.