How to drive a malware analyst crazy
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This document discusses techniques that malware authors use to frustrate malware analysts, including inserting breakpoints, manipulating timing functions, exploiting Windows internals like debug flags and objects, anti-dumping methods, VM detection, and debugger-specific tricks. The author also announces a public malware repository and API called VXCage for sharing samples.
![About me
4th year speaking at 44CON
- 2012: Malware as a hobby [P]
- 2013: Controlling a PC using Arduino [WS]
- 2014: Malware analysis as a big data problem [P]
- 2015: Malware anti-reversing [P], Indicators of Compromise [WS]
Malware Researcher, Founder Malware Research Institute
6 kids, one more on the way…](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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How to drive a malware analyst crazy
- 1. How to drive a malware analyst crazy MICHAEL BOMAN, MALWARE RESEARCH INSTITUTE
- 2. About me 4th year speaking at 44CON - 2012: Malware as a hobby [P] - 2013: Controlling a PC using Arduino [WS] - 2014: Malware analysis as a big data problem [P] - 2015: Malware anti-reversing [P], Indicators of Compromise [WS] Malware Researcher, Founder Malware Research Institute 6 kids, one more on the way…
- 3. Malware Research Lab, 2012
- 4. Malware Research Lab, 2015
- 5. Disclaimer These are the techniques I’ve come across trying to keep malware researchers out of the game Or just waste a heck of a lot time doing quite silly things… Not a complete list of techniques The techniques discussed are aimed towards a x86/win32 environment
- 6. Technique #1: Breakpoints INT 3h Memory Breakpoints Hardware Breakpoints
- 7. How INT3 breakpoints work mov eax, fs:[0x30] mov eax, [eax + 0x0c] // <- Break here mov eax, [eax + 0x0c] mov dword ptr [eax + 0x20], NewSize
- 8. How INT3 breakpoints work mov eax, fs:[0x30] int 3h [garbage] // <- EP mov eax, [eax + 0x0c] mov dword ptr [eax + 0x20], NewSize
- 9. How INT3 breakpoints work mov eax, fs:[0x30] mov eax, [eax + 0x0c] // <- restored by debugger mov eax, [eax + 0x0c] mov dword ptr [eax + 0x20], NewSize
- 10. Memory Breakpoints Allocate memory, mark PAGE_GUARD When accessed STATUS_GUEARD_PAGE_VIOLATION is raised, handled by program Allocate memory as buffer Fill buffer with RET instruction Mark buffer with PAGE_GUARD PUSH potential return address to stack JMP to buffer If debugger: RET will jump back to potential return address else: STATUS_GUARD_PAGE_VIOLATOIN exception occur
- 11. Hardware breakpoints Hardware breakpoints are a technology implemented by Intel in their processor architecture, and are controlled by the use of Special registers DR0 - DR7 DR0 - DR3 - 32 bit registers for the breakpoint address DR4, DR5 - obsolete synonyms for DR6 and DR7 DR6 – Debug status DR7 – Debug control
- 12. Technique #1: Breakpoints INT 3h Look for code that scans memory for 0xCC [INT3] and/or 0xCD 0x03 [INT (immediate) 3] Memory Breakpoints Look for memory allocations with PAGE_GUARD flag set Hardware Breakpoints Win32 GetThreadContext and SetThreadContext Structured Exception Handling
- 13. Technique #2: Timing RDTSC (ReaD TimeStampClock) Win32 Timing Functions GetTickCount timeGetTime QueryPerformanceCounter […]
- 14. Technique #2: Timing RDTSC (ReaD TimeStampClock) Mark RDTSC as a elevated instruction (can then be intercepted and modified) Win32 Timing Functions Use DLL-injection to overload the function with one that lies nicely in our favour Please remember to lie consistently to all timing methods.
- 15. Technique #3: Windows Internals ProcessDebugFlags Debug Object Handle Thread Hiding BlockInput OutputDebugString
- 16. ProcessDebugFlags Pass undocumented class ProcessDebugFlags (0x1f) to the NtQueryProcessInformation() function. When NtQueryProcessInformation is called with the ProcessDebugFlags class, returns the inverse of EPROCESS -> NoDebugInherit FALSE == Debugger present
- 17. Debug Object Handle Windows XP or later When debugged a Debug Object created Can be queried using NtQueryInformationProcess Originating from kernel -> hard to hide
- 18. Thread Hiding Windows 2000 and later HideThreadFromDebugger class, passed into NtSetInformationThread, The class prevents debuggers from receiving events from any thread that has had NtSetInformationThread with the HideThreadFromDebugger class called on it. These events include breakpoints, and the exiting of the program if it is called on the main thread of an application.
- 19. BlockInput BlockInput() blocks mouse and keyboard messages from reaching the desired application Only the thread that called BlockInput can call it to remove the block Not really Anti-RE, but can mess with you
- 20. OutputDebugString Call OutputDebugString() GetLastError() No error == debugger present
- 21. Technique #3: Windows Internals ProcessDebugFlags Check NtQueryProcessInformation() calls for [undocumented] ProcessDebugFlags (0x1f) object Hook NtQueryProcessInformation(), lie about the ProcessDebugFlags value Debug Object Handle Hook NtQueryInformationProcess(), remove any links to debug objects Thread Hiding Remove any HideThreadFromDebugger class passed into NtSetInformationThread BlockInput Hook it to a NO-OP OutputDebugString Hook it to always return error
- 22. Technique #4: Process Exploitation Open Process Parent Process Self-Debugging UnhandledExceptionFilter NtQueryObject
- 23. Open Process Debugger not properly resets process privileges Open privileged process like csrss.exe If succeed we are running under a debugger
- 24. Parent Process Check if GetParentProcessId() and GetExplorerPIDbyShellWindow()) is the same Or however you are expecting your malware to be executed
- 25. Self-Debugging Parent spawns child who debugs the parent Prevents debugger to attach to parent Child Parent
- 26. UnhandledExceptionFilter UnhandledExceptionFilter is the exception handler that is called when there are no other handlers to handle the exception. When utilizing this technique, the process will exit instead of resuming execution which is fine for Anti-RE purposes. UnhandledExceptionFilter SEH Chain Vectored Exception Handlers
- 27. NtQueryObject NtQueryObject() called with ObjectAllTypesInformation class, returns information about the host system and the current process including DebugObjects in the environment. ObjectAllTypesInformation can be traversed to locate DebugObjects
- 28. Technique #4: Process Exploitation Open Process – Make sure debugger drops SeDebugPrivilege Parent Process – Fake GetParentProcessId() Self-Debugging - Set PsGetProcessId()->EPROCESS->DebugPort to 0 UnhandledExceptionFilter – Make sure the debugger do “the right thing” NtQueryObject – Intercept and filter
- 29. Technique #5: Anti-dumping Nanomites Stolen Bytes (Stolen Code) SizeOfImage Virtual Machines Guard Pages Removing the PE Header
- 30. Nanomites Replace JUMP (Jxx) instructions with INT 3h breakpoints Store original JUMP (Jxx) instruction in an encrypted table Use self-debugging, debugger process will substitute the INT 3h code with the correct JUMP instruction depending on encryption algorithm. Put some stray INT 3h in the execution flow and you have made a real mess
- 31. Stolen Bytes (Stolen Code) Code or bytes from the original process protected by the packer are copied and encrypted somewhere inside the packing code The original (copied) code is replaced with jumps to a dynamic allocated buffer for the decrypted bytes and then jumps back to the original flow
- 32. SizeOfImage Modifying PE -> IMAGE_OPTION_HEADER -> SizeOfImage can cause problems for tools that weren't developed to handle this problem.
- 33. Virtual Machines (think JVM, not VBox) Protectors like Themida and VMProtect already use virtual machines in their protection schemes. Themida uses a technology that creates a unique virtual machine for every protected executable Prevents the use of a generic attack against its virtualization protection Many protection schemes implement junk code instructions
- 34. Guard Pages Discussed earlier Can be used for an on-demand decryption/decompression system Mark all pages that were not immediately needed as guard pages When accessed, an EXCEPTION_GUARD_PAGE exception will be raised Additional data can be decrypted or decompressed either from file or memory.
- 35. Removing the PE Header Removes an executable's portable executable from memory at runtime A dumped image would be missing important information such as the RVA (Relative Virtual Address) of important tables (Reloc, Import, Export etc..), the entry point, and other information that the Windows loader needs to utilize when loading an image
- 36. Technique #5: Anti-dumping Nanomites Stolen Bytes (Stolen Code) SizeOfImage Virtual Machines Guard Pages Removing the PE Header
- 37. Technique #6: Exploiting IA-32 Instructions Interrupt 2D Stack Segment Instruction Prefixes
- 38. Interrupt 2D INT 2D instruction can be used as a debugger detection method When executed No Debugger Present -> Exception Debugger Present -> No Exception Debugger specific
- 39. Stack Segment Manipulate stack segment using push ss and pop ss cause the debugger to execute instructions unwillingly In the following code, when stepping over the code with any debugger, the mov eax, 9 line will execute, but will not be stepped on by the debugger. push ss pop ss mov eax, 9 // This line executes but is stepped over xor edx, edx // This is where the debugger will step to
- 40. Instruction Prefixes Takes advantage of the way debuggers handle instruction prefixes. When stepping over this code in OllyDBG or in Visual Studio 2008, we will reach the first emit and immediately be taken to the end of the __try block. What happens is that the debugger essentially skips over the prefix and handles the INT 1. When running this code without a debugger, there will be an exception that SEH will catch and the program will continue along. inline bool IsDbgPresentPrefixCheck() { __try { __asm __emit 0xF3 // 0xF3 0x64 disassembles as PREFIX REP: __asm __emit 0x64 __asm __emit 0xF1 // One byte INT 1 } __except(EXCEPTION_EXECUTE_HANDLER) { return false; } return true; }
- 41. Technique #6: Exploiting IA-32 Instructions Interrupt 2D Stack Segment Instruction Prefixes
- 42. Technique #7: VM Detection VM Artefacts Hardware Drivers OS version / serial number Add-ons WMI calls Interactivity Is the computer being used? Click on invisible or very small buttons no human could see
- 43. Technique #7: VM Detection VM Artefacts Hardware – Clone real system configuration Drivers – Don’t use VM-specific drivers OS version / serial number – Use ”real” serial numbers Add-ons – Never install VM Guest tools WMI calls – Patch hypervisor, use real hardware Interactivity Is the computer being used? – Fake interactivity Click on invisible or very small buttons no human could see – Make sure your fake interactivity is plausible
- 44. Debugger specific techniques OllyDBG FindWindow OutputDebugString Exploit WinDBG FindWindow Cuckoo Sandbox Check if hooked
- 45. Debugger specific techniques OllyDBG FindWindow – Hijack function call or modify OllyDBG binary OutputDebugString Exploit – Run patched version WinDBG FindWindow – Hijack function call or modify WinDBG binary Cuckoo Sandbox Check if hooked – Run unhooked, patch the hook-check function
- 46. Other Techniques Junk Code Native Code Permutations
- 47. Other Techniques Junk Code Native Code Permutations Unfortunately there are no quick-fixes for these techniques
- 49. Announcement Public VXCage-server Available at vxcage.malwareresearch.institute (http, soon https) Feel free to apply for a personal account, free of charge: TO: michael@michaelboman.org SUBJECT: VXCage Access BODY: Who you are: name, twitter handle (if any, for cyberstalking), other contact info Why you want access Proposed username for the system (the password will be generated for you) Please contact me at the above address for raw access to the archive
- 50. VXCage API: Quick intro REST with JSON output /malware/add – upload sample /malware/get/<sha256> - download sample /malware/find – search sample based on hash, date, tag /tags/list – list tags Docs & Source code at https://github.com/mboman/vxcage
- 51. Thank you Michael Boman (@mboman) michael@michaelboman.org (soon also michael.boman@malwareresearch.institute) Malware repository: vxcage.malwareresearch.institute Malware blog: blog.malwareresearch.institute