This document discusses anti-virus evasion techniques and countermeasures. It explains how to split malware execution into two parts - a standalone executable code and an interface to execute that code - in order to bypass signature-based and emulation-based antivirus detection. It provides three techniques for the interface: code injection into another process, jumping and executing the code, and using loaders. It also discusses how antiviruses can detect these techniques through shellcode detection and provides a demonstration of shellcode detection.

1. Amit Malik (DouBle_Zer0) SecurityXploded and Garage4hackers Bangalore Chapter Lead E-Mail: m.amit30@gmail.com Anti-Virus Evasion techniques and Countermeasures

2. Why How Countermeasure Legal Statement  Agenda

3. I am a Penetration Tester. I want to use public codes* without fear. I want to know the system internals. I want to impress my girl friend ^_^. I want to test effectiveness of security technologies. WHY

4. Warning: Everything that I will discuss here is not applicable to .exe files. Logic – divide exe in two parts – means don’t make exe. Code Interface Code – it is our normal code with some additional powers – stand alone executable code. Interface - interface will execute the code In simple words we need a shellcode type code and a interface to execute the shellcode. HOW #1

5. Why we are splitting exe in two parts ? AV detection techniques Signature based Emulation + signature MD5  Heuristic  If your binary is packed then AV uses Emulation + signature tech. for detection. By splitting exe in two parts we can bypass AVs. True fact: generating exe is simpler than writing the stand alone executable code that performs the same function.  HOW #2

6. Techniques: Code injection in another process Jump and Execute Loaders HOW #3

7. Code injection in another process Interface – make a interface that will read the “code” and will inject it into another process. Raw Material: OpenProcess WriteProcessMemory CreateRemoteThread HOW #4 – Technique #1

8. HOW #4 – Technique #1 - Demo

9. Jump and Execute Interface – make a interface that will read the file and then jump to that location and execute the code Raw Material: ReadFile JMP HOW #4 – Technique #2

10. HOW #4 – Technique #2 - Demo

11. Loaders Interface – make a interface that will read the “code” and creates a trusted process in suspended mode and overwrite the “code” at the entry point of the suspended process and then resume the thread. Raw Material: CreateProcess – suspended WriteProcessMemory ResumeThread HOW #4 – Technique #3

12. HOW #4 – Technique #3 -Demo

13. What if AV flag Interface ? Yes, they can but the interface code is using legitimate APIs with very minimal code. Many legitimate programs use similar APIs so fear of false positive. May be they can flag on the basis of MD5  HOW #5

14. Simply call it shellcode detection The Philosophy Emulate or Execute Everything Exception – move to next byte Abort execution if anytime EIP >= 7xxxxxxx Scan – Detection Countermeasures

15. Shellcode Detection - Demo

16. “Shellcode Detection” Technique and source codes are distributed under CC. http://creativecommons.org/licenses/by-nc/3.0/ Codes: https://sites.google.com/site/hacking1now/tools Legal Statement