Patent Application
20090328011
To protect against malicious content, intrusion prevention systems (and similarly intrusion detection systems) use an engine that includes logic for evaluating incoming (and outgoing) network traffic against signatures to detect patterns of known malicious content. Traditionally, signatures in intrusion prevention systems are described by a set of complex data structures describing how to distinguish legitimate valid data from data corresponding to an attempted attack.
One problem with this approach is based on the signature schema. More particularly, because of the schema, the signature language may not be able to express the state identifying the vulnerability, or can only do so via very complex coding.
Further, to include the logic for various protocols and signature processing, the engine may be a complex, relatively heavyweight mechanism. The engine needs to be maintained, and updated from time to time as new logic to detect new signatures is developed.
This Summary is provided to introduce a selection of representative concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used in any way that would limit the scope of the claimed subject matter.
Briefly, various aspects of the subject matter described herein are directed towards a technology by which a signature to detect is compiled into executable logic that helps in detecting that signature. The executable logic of the signature is used to direct a network intrusion detection/intrusion prevention engine that evaluates network traffic to look for matches. To this end, the engine communicates with (e.g., calls into) the signature logic to receive an expression set (such as group of regular expressions) from that logic and detects whether a token corresponding to the network traffic matches the expression set. If so, the engine notifies the logic and receives a further expression to match, or a communication indicative that that the signature was detected.
In one aspect, safety of the signature logic is described as being accomplished through layers. For example, in addition to being signed by the publisher, the signature may be authored in a definition language, which is compiled by a safe compiler into source code, which in turn is compiled into intermediate language code. The intermediate language code is executed via an interpreter or a framework (e.g., .NET) that helps protect its surrounding system.
Other advantages may become apparent from the following detailed description when taken in conjunction with the drawings.
The present invention is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which:
Various aspects of the technology described herein are generally directed towards compiling signatures into code, including the logic that is executed to evaluate traffic for the signatures. Schema-related problems are avoided, while at the same time allowing a lightweight engine to be used to execute the signatures. Because the logic is in the signatures, the engine need not be updated, e.g., as protocols, logic and/or signatures change.
While the various examples herein are directed towards detecting malicious code in an intrusion prevention/intrusion detection system environment, these are only examples. Other uses of parsing data and evaluating that data via logic may benefit from the technology described herein. As such, the present invention is not limited to any particular embodiments, aspects, concepts, structures, functionalities or examples described herein. Rather, any of the embodiments, aspects, concepts, structures, functionalities or examples described herein are non-limiting, and the present invention may be used various ways that provide benefits and advantages in computing and network traffic analysis in general.
Turning to
By way of example, the analyzer 104 may communicate with some logic to determine that a comma token is to be detected, and when detected, may communicate again to determine that two consecutive slash characters should next be detected, and so on. The logic may be more complex than simply providing a next expression set to match, but in general, the analyzer 104 parses and/or matches data as directed by the logic. Also, the analyzer 104 provides an API for coupled logic to get and set variables, and/or specify that part of the network traffic is to be buffered, e.g., rather than simply having the analyzer discard data (e.g., characters) that are not matches with the expression currently specified by the logic.
In one implementation, the compiler 222 includes a two-level compilation process, namely a GAPA compiler 230 that processes the definition language 220 into a source code in a language such as C++, and a compiler 232 that takes the generated source code and processes it into an intermediate language, such as MSIL (Microsoft® Intermediate Language); note that compilers already exist that produce MSIL code from C++ or C#, such as provided by Microsoft Corporation.
One consideration when dealing with executable code is safety. The delivered machine code must not be able to do harm (either as a result of intentional attack or due to a human mistake) the system. Thus, in one implementation, the safety of the machine code in a signature is guaranteed, to an extent, by requiring that the compiled signature be signed by the publisher's certificate.
While it is a feasible alternative to compile the source code directly into machine code, this is not particularly safe, as the machine code may be able to harm the system, with only the signed certificate as a guarantee of safety, which may help against intentional malicious code, but not erroneous malicious code. It is also a feasible alternative to compile the source code into a proprietary language for a proprietary interpreter, however again this is not particularly transparent with respect to safety, and adds complexity.
Thus, in one implementation, the analyst authoring the source code does not write it for direct compilation. Instead the signature is developed on a safe programming environment, such as using a subset of the C++ language that is verified to use only safe constructions. For example, because Microsoft® C++/CLI or C# compilers exist that produce MSIL code, by transforming GAPA language to managed C++ or C# (restricted to safe constructions only) and using an already existing compiler, to obtain the machine or intermediate code.
Further, because the source code is compiled into an intermediate languages, such as MSIL, the code can be safely executed within an interpreter 250, e.g., contained in the engine 102, or through the .NET Framework. Either approach further ensures that the delivered signature logic 224 (intermediate code) cannot harm the system in which it is running. Moreover, the MSIL opcode set has been proven to be reasonably good and robust.
To summarize, safety is provided in layers in one example implementation; signature is signed by a publisher, and the C++ code is not developed directly, but is generated by a tool that does not use “dangerous” C++ constructions like pointer arithmetic. The compiler may be configured to validate that only safe code is produced. The interpreter or NET Framework (virtual machine) running MSIL code verifies that only valid operations are executed.
As can be readily appreciated, by being arranged as executable code in the above manner, the signature logic 224 can express virtually any safe logic. At the same time, the IPS/IDS engine 102 is very lightweight and easier to maintain because the logic is in the delivered code rather than built into the engine. This is advantageous, as keeping most of the complex logic in analyst tools rather than in the IPS/IDS engine reduces the cost of software maintenance. Further, as can be readily appreciated, in this model there are no abstraction layers and/or adapters, providing good performance.
As a result, the IPS engine 102 comprises a mostly generic component shipped to the end user as a product that rarely needs changing. By providing the logic as part of the signature in this model, the IPS engine 102 is developed in advance to be flexible to handle future attacks yet to be discovered.
Turning to aspects of operation, each signature implements a state machine (e.g., a push down automata implementing an LL(1) parser). The engine 102, via the analyzer 104, is responsible for tokenizing the input according to regular expressions specified inside the signature logic 224, and letting the state machine code carried with the signature track the state of the protocol, firing a “signature match” event upon a specific condition being matched.
This is generally represented in
As can be readily appreciated, coding the signature ensures that the GAPA-based engine need not be aware of the actual algorithms involved in matching signatures to the network traffic. The overall operation is very generic, leaving the specific details of how parsing for a signature is done to the signature itself, which is easily updated by delivering a new set of signatures. This operation is very lightweight and completely transparent to the end-user.
It is typical that providing a more generic evaluation engine decreases performance. However, moving the pieces of code that are not expected to change to the engine for processing as native code instead of as interpreted code will improve performance.
Step 410 represents verifying the publisher, which in addition to the compilation steps provides layered security. If the publisher is OK, step 412 represents the engine's communication with the logic to receive an expression to evaluate as possibly being part of a signature. The processing/parsing continues until the expression is matched.
When matched, further communication with the logic is performed, generally to obtain the next expression to match, or to determine (step 418) whether the signature was fully detected, and if so, to output an indication (step 420), such as to an application. In general, the evaluation engine continues to communicate with the executable signature to obtain an expression to match for signature evaluation.
The invention is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well known computing systems, environments, and/or configurations that may be suitable for use with the invention include, but are not limited to: personal computers, server computers, hand-held or laptop devices, tablet devices, multiprocessor systems, microprocessor-based systems, set top boxes, embedded systems, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like.
The invention may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, and so forth, which perform particular tasks or implement particular abstract data types. The invention may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in local and/or remote computer storage media including memory storage devices.
With reference to
The computer 510 typically includes a variety of computer-readable media. Computer-readable media can be any available media that can be accessed by the computer 510 and includes both volatile and nonvolatile media, and removable and non-removable media. By way of example, and not limitation, computer-readable media may comprise computer storage media and communication media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by the computer 510. Communication media typically embodies computer-readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of the any of the above may also be included within the scope of computer-readable media.
The system memory 530 includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM) 531 and random access memory (RAM) 532. A basic input/output system 533 (BIOS), containing the basic routines that help to transfer information between elements within computer 510, such as during start-up, is typically stored in ROM 531. RAM 532 typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit 520. By way of example, and not limitation,
The computer 510 may also include other removable/non-removable, volatile/nonvolatile computer storage media. By way of example only,
The drives and their associated computer storage media, described above and illustrated in
The computer 510 may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer 580. The remote computer 580 may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer 510, although only a memory storage device 581 has been illustrated in
When used in a LAN networking environment, the computer 510 is connected to the LAN 571 through a network interface or adapter 570. When used in a WAN networking environment, the computer 510 typically includes a modem 572 or other means for establishing communications over the WAN 573, such as the Internet. The modem 572, which may be internal or external, may be connected to the system bus 521 via the user input interface 560 or other appropriate mechanism. A wireless networking component such as comprising an interface and antenna may be coupled through a suitable device such as an access point or peer computer to a WAN or LAN. In a networked environment, program modules depicted relative to the computer 510, or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation,
An auxiliary subsystem 599 (e.g., for auxiliary display of content) may be connected via the user interface 560 to allow data such as program content, system status and event notifications to be provided to the user, even if the main portions of the computer system are in a low power state. The auxiliary subsystem 599 may be connected to the modem 572 and/or network interface 570 to allow communication between these systems while the main processing unit 520 is in a low power state.
While the invention is susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention.
