Cheat Sheet for Analyzing Malicious Software

This cheat sheet presents tips for analyzing and reverse-engineering malware. It outlines the steps for performing behavioral and code-level analysis of malicious software.

Overview of the Malware Analysis Process

1. Use automated analysis sandbox tools for an initial assessment of the suspicious file.
2. Set up a controlled, isolated laboratory in which to examine the malware specimen.
3. Examine static properties and meta-data of the specimen for triage and early theories.
4. Perform behavioural analysis to examine the specimen’s interactions with its environment.
5. Perform static code analysis to further understand the specimen’s inner-workings.
6. Perform dynamic code analysis to understand the more difficult aspects of the code.
7. If necessary, unpack the specimen.
8. Perform memory forensics of the infected lab system to supplement the other findings.
9. Repeat steps 4-8 above as necessary (the order may vary) until analysis objectives are met.
10. Document findings, save analysis artifacts and clean-up the laboratory for future analysis.

Behavioral Analysis

• Be ready to revert to good state via virtualization snapshots, Clonezilla, dd, FOG, PXE booting, etc.
• Monitor local interactions (Process Explorer, Process Monitor, ProcDOT, Noriben).
• Detect major local changes (RegShot, Autoruns).
• Monitor network interactions (Wireshark, Fiddler).
• Redirect network traffic (fakedns, FakeNet-NG).
• Activate services (INetSim or actual services) requested by malware and reinfect the system.
• Adjust the runtime environment for the specimen as it requests additional local or network resources.

Ghidra for Static Code Analysis

x64dbg/x32dbg for Dynamic Code Analysis

Unpacking Malicious Code

• Determine whether the specimen is packed by using Detect It Easy, Exeinfo PE, Bytehist, peframe, etc.
• To try unpacking the specimen quickly, infect the lab system and dump from memory using Scylla.
• For more precision, find the Original Entry Point (OEP) in a debugger and dump with OllyDumpEx.
• To find the OEP, anticipate the condition close to the end of the unpacker and set the breakpoint.
• Try setting a memory breakpoint on the stack in the unpacker’s beginning to catch it during cleanup.
• To get closer to the OEP, set breakpoints on APIs such as LoadLibrary, VirtualAlloc, etc.
• To intercept process injection set breakpoints on VirtualAllocEx, WriteProcessMemory, etc.
• If cannot dump cleanly, examine the packed specimen via dynamic code analysis while it runs.
• Rebuild imports and other aspects of the dumped file using Scylla, Imports Fixer, UIF, pe_unmapper.

Bypassing Other Analysis Defenses

• Decode obfuscated strings statically using FLARE, xorsearch, Balbuzard, etc.
• Decode data in a debugger by setting a breakpoint after the decoding function and examining results.
• Conceal x64dbg/x32dbg via the ScyllaHide plugin.
• To disable anti-analysis functionality, locate and patch the defensive code using a debugger.
• Look out for tricky jumps via TLS, SEH, RET, CALL, etc. when stepping through the code in a debugger.
• If analyzing shellcode, use scdbg and jmp2it.
• Disable ASLR via setdllcharacteristics, CFF Explorer.

credits: L Zeltser