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. To print it, use the one-page PDF version; you can also edit the Word version to customize it for you own needs.

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 behavioral 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

IDA Pro for Static Code Analysis

Text searchAlt+t
Show strings windowShift+F12
Show the operand as a characterr
Insert repeatable comment;
Follow jump or call in viewEnter
Return to previous viewEsc
Go to next viewCtrl+Enter
Toggle between text and graph viewsSpacebar
Display a diagram of function callsCtrl+F12
List program’s entry point(s)Ctrl+e
Go to specific addressg
Rename a variable or functionn
Show cross-references to selected functionSelect function name » x

x64dbg/x32dbg for Dynamic Code Analysis

Run the codeF9
Step into/over instructionF7 / F8
Execute until selected instructionF4
Execute untill next returnCtrl+F9
Show previous/next executed instruction– / +
Return to previous view*
Go to specific expressionCtrl+g
Insert comment/label; / :
Show current function as a graphg
Find specific patternCtrl+b
Set software breakpoint on specific instructionSelect instruction » F2
Set software breakpoint on APIGo to Command prompt » SetBPX API Name
Highlight all occurrences of the keyword in disassemblerh » Click on keyword
Assemble instruction in place of selected oneSelect instruction » Spacebar
Edit data in memory or instruction opcodeSelect data or instruction » Ctrl+e
Extract API call referencesRight-click in disassembler » Search for » Current module » Intermodular calls

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.

Post-Scriptum

If you have suggestions for improving this cheat sheet, please let me know. Creative Commons v3 “Attribution” License for this cheat sheet version 2.0.

Updated

About the Author

Lenny Zeltser is a seasoned business and technology leader with extensive information security experience. He builds innovative endpoint defense solutions as VP of Products at Minerva Labs. He also trains incident response and digital forensics professionals at SANS Institute. Lenny frequently speaks at industry events, writes articles and has co-authored books. He has earned the prestigious GIAC Security Expert designation, has an MBA from MIT Sloan and a Computer Science degree from the University of Pennsylvania.

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