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Viruses like Virut are fascinating examples of self-replicating malware that have persisted for years. This analysis covers key techniques for reverse-engineering Virut, including handling self-modifying code, API resolution, and Ghidra patching.
🔗 Video Tutorial: Malware Analysis – Virut, a Polymorphic File Infector
You Should Know:
1. Dealing with Self-Modifying Code
Virut uses polymorphism to evade detection, meaning its code changes dynamically. To analyze it:
– Use a debugger like x64dbg or OllyDbg to trace execution.
– Set memory breakpoints to catch decryption routines.
Monitor memory access in GDB (Linux) gdb -q ./virut_sample (gdb) watch 0x00401000 Break on code modification (gdb) continue
2. Creating an API Resolver in Python
Virut resolves APIs dynamically. Emulate this with Python:
import ctypes Example: Resolving kernel32!CreateFileA kernel32 = ctypes.windll.kernel32 CreateFileA = kernel32.CreateFileA CreateFileA.argtypes = [ctypes.c_char_p, ctypes.c_uint32, ctypes.c_uint32, ctypes.c_void_p, ctypes.c_uint32, ctypes.c_uint32, ctypes.c_void_p]
3. Forcing Win10 Execution via Patching
Virut may check OS version. Patch it using HxD or Ghidra:
– Locate `GetVersionExA` calls.
– Modify return values to spoof Windows 10.
4. Ghidra Markup & Database Patching
- Decompile Virut’s decryption stub in Ghidra.
- Patch Ghidra’s database if analysis fails:
Backup Ghidra project cp -r /path/to/project /backup_location
What Undercode Say:
Polymorphic malware like Virut remains a challenge due to its adaptive nature. Key takeaways:
– Dynamic Analysis is Critical: Use debuggers to catch runtime changes.
– API Hooking Helps: Tools like Frida or Detours can intercept Virut’s API calls.
– Ghidra Scripting: Automate decryption logic with Python scripts.
Relevant Commands:
Linux memory forensics (if Virut infects ELF) volatility -f memory_dump.raw --profile=LinuxUbuntu_5x pslist
Windows: Check for Virut artifacts
Get-ChildItem -Path C:\Windows\ -Recurse -Force | Where-Object { $_.Length -gt 10MB }
Expected Output:
A fully unpacked Virut sample with annotated Ghidra disassembly, dynamic API logs, and patched execution path for modern OS compatibility.
🔗 Additional Resources:
References:
Reported By: Karsten Hahn – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
