Low-latency detection of scripting-language-based exploits
Systems and methods for protecting client computers are described. One method includes receiving webpage data at a proxy from a webpage before the data reaches an intended recipient; gathering scripting-language-data from the webpage data; normalizing the scripting-language-data so as to generate normalized data; emulating execution of the normalized scripting-language-data with a inspection-point-script-execution engine that that is adapted to provide inspection points instead of effectuating particular functions, and determining whether to block the data from the intended recipient by analyzing inspection-data collected from the inspection points.
1. A method for protecting client computers, comprising:
receiving webpage data at a proxy from a webpage before the data reaches an intended recipient, wherein the proxy is disposed as an intermediary between a server serving up the webpage and the intended recipient;
gathering scripting-language-data from the webpage data;
normalizing the scripting-language-data so as to generate normalized data;
emulating execution of the normalized scripting-language-data with a inspection-point-script-execution engine adapted to provide inspection points instead of effectuating particular functions, wherein an inspection point comprises one or more collections of inspection-data, the inspection-data comprising data collected from emulating the execution of the scripting-language-data and including an indication of one or more emulated functions; and
determining whether to prevent the data from reaching the intended recipient by analyzing inspection-data collected from the inspection points.
2. The method of claim 1 , including:
disassembling a string that is generated during the normalizing of scripting-language-data;
pseudo-executing the disassembled string; and
determining whether the scripting-language-data includes shellcode.
3. The method of claim 2 , wherein the disassembling is responsive to a size of the string exceeding a threshold.
4. The method of claim 1 , including:
modifying an existing script-execution engine so that objects in the existing script-execution engine that are intended to provide functions are overwritten to provide inspection-data instead of the functions.
5. The method of claim 1 , including:
identifying characteristics of the normalized scripting-language-data;
scoring the characteristics of the normalized scripting-language-data based upon a likelihood that the characteristics of the normalized scripting-language-data are associated with malicious scripting-language-data;
scoring characteristics of the inspection-data based upon a likelihood that the characteristics of the inspection-data are associated with malicious scripting-language-data; and
determining whether to block the data from the intended recipient based upon the scoring of the characteristics of the normalized scripting-language-data and the scoring of the characteristics of the inspection-data.
6. The method of claim 5 , wherein identifying characteristics of the normalized scripting-language-data includes identifying a presence of Eval functions, identifying statements exceeding a threshold-string-size, and identifying the existence of a DOM object, and wherein the inspection-data collected from the inspection points includes an indication whether a hidden Iframe is present, an indication whether a script writes another dynamic script, and an indication whether a script error matches a known anti-emulator method.
7. The method of claim 2 , including:
identifying characteristics of the normalized scripting-language-data;
scoring the characteristics of the normalized scripting-language-data based upon a likelihood that the characteristics of the normalized scripting-language-data are associated with malicious scripting-language-data;
scoring characteristics of the inspection-data based upon a likelihood that the characteristics of the inspection-data are associated with malicious scripting-language-data; and
determining whether to block the data from the intended recipient based upon the scoring of the characteristics of the normalized scripting-language-data, the scoring of the characteristics of the inspection-data, and the determination whether the scripting-language-data includes shellcode.
8. The method of claim 1 , including:
tracking a variable during the emulated execution;
delaying a storage of inspection-data from an inspection point until a scope of the variable is lost.
9. The method of claim 1 , wherein emulating execution of the normalized scripting-language-data includes emulating a DOM.
10. A system for protecting client computers, comprising:
an initial filter that gathers scripting-language-data from webpage data;
an interpretation component that obtains inspection-data from the scripting-language-data by emulating execution of the scripting-language-data the inspection-data further including an indication of one or more emulated functions;
a shellcode module that disassembles one or more strings that are generated during the emulated execution of the scripting-language-data so as to generate disassembled code and pseudo-executes at least a portion of the disassembled code to determine whether to block the scripting-language-data from reaching an intended recipient based upon pseudo-execution-data; and
an analysis component that assesses the inspection-data to determine whether to block the scripting-language-data from reaching the intended recipient.
11. The system of claim 10 , wherein the initial filter includes:
a script consolidation portion that consolidates separated pieces of the scripting-language-data so as to generate consolidated scripting-language-data; and
a parser that tokenizes the consolidated scripting-language-data to obtain scripting-language-data that is tokenized, wherein the interpretation component emulates execution of the scripting-language-data that has been tokenized.
12. The system of claim 10 , wherein the interpretation component delays obtaining the inspection-data until a scope of a tracked-variable is lost.
13. The system of claim 10 , wherein the interpretation component includes a scripting-language engine that is adapted so that objects that would ordinarily provide functions for the scripting-language-data provide inspection points to enable acquisition of the inspection-data.
14. The system of claim 10 , wherein the shellcode module does not disassemble the one or more strings unless the one or more strings exceeds a size threshold.
15. The system of claim 10 , including identifying suspect regions in the disassembled code and pseudo-executing the suspect regions.
16. A method for protecting client computers, comprising:
receiving webpage data at a proxy from a webpage before the data reaches an intended recipient, wherein the proxy is disposed as an intermediary between a server serving up the webpage and the intended recipient;
gathering scripting-language-data from the webpage data;
prompting the scripting-language-data to unpack into one or more strings;
normalizing one or more unpacked strings;
disassembling one or more of the normalized strings that are suspected of including shell code;
determining, without pseudo-executing, whether the disassembled suspect string indicates that scripting-language-data should be blocked; and
pseudo-executing the disassembled suspect string if the string cannot be determined to be safe.
17. The method of claim 1 , wherein the proxy and the intended remote user are communicatively coupled through the Internet.
18. The method of claim 1 , wherein the intended recipient is a remote user.
19. The system of claim 10 , wherein the intended recipient is located at a location remote from the system for protecting client computers.
20. The method of claim 16 , wherein the proxy and the intended remote user are communicatively coupled through the Internet.