Reverse-Engineering Malware Cheat Sheet

This is a cheat sheet of shortcuts and tips for reverse-engineering malware. It covers the general malware analysis process, as well as useful tips for OllyDbg, IDA Pro, and other tools. Feel free to customize it to your own needs. My reverse-engineering malware course explores these, and other useful techniques. To print, use the one-sheet PDF version; you can also edit the Word version for you own needs. If you like this, take a look at my other IT cheat sheets.

General Approach

  1. Set up a controlled, isolated laboratory in which to examine the malware specimen.
  2. Perform behavioral analysis to examine the specimen’s interactions with its environment.
  3. Perform static code analysis to further understand the specimen’s inner-workings.
  4. Perform dynamic code analysis to understand the more difficult aspects of the code.
  5. If necessary, unpack the specimen.
  6. Repeat steps 2, 3, and 4 (order may vary) until sufficient analysis objectives are met.
  7. Document findings and clean-up the laboratory for future analysis.

Behavioral Analysis

IDA Pro for Static Code Analysis

Text search Alt+T
Show strings window Shift+F12
Show operand as hex value Q
Insert comment :
Follow jump or call in view Enter
Return to previous view Esc
Go to next view Ctrl+Enter
Show names window Shift+F4
Display function’s flow chart F12
Display graph of function calls Ctrl+F12
Go to program’s entry point Ctrl+E
Go to specific address G
Rename a variable or function N
Show listing of names Ctrl+L
Display listing of segments Ctrl+S
Show cross-references to selected function Select function name » Ctrl+X
Show stack of current function Ctrl+K

OllyDbg for Dynamic Code Analysis

Step into instruction F7
Step over instruction F8
Execute till next breakpoint F9
Execute till next return Ctrl+F9
Show previous executed instruction -
Show next executed instruction +
Return to previous view *
Show memory map Alt+M
Follow expression in view Ctrl+G
Insert comment ;
Follow jump or call in view Enter
Show listing of names Ctrl+N
New binary search Ctrl+B
Next binary search result Ctrl+L
Show listing of software breakpoints Alt+B
Assemble instruction in place of selected one Select instruction » Spacebar
Edit data in memory or instruction opcode Select data or instruction » Ctrl+E
Show SEH chain View » SEH chain
Show patches Ctrl+P

Bypassing Malware Defenses

  • To try unpacking quickly, infect the system and dump from memory via LordPE or OllyDump.
  • For more surgical unpacking, locate the Original Entry Point (OEP) after the unpacker executes.
  • If cannot unpack cleanly, examine the packed specimen via dynamic code analysis while it runs.
  • When unpacking in OllyDbg, try SFX (bytewise) and OllyDump’s “Find OEP by Section Hop”.
  • Conceal OllyDbg via HideOD and OllyAdvanced.
  • A JMP or CALL to EAX may indicate the OEP, possibly preceded by POPA or POPAD.
  • Look out for tricky jumps via SEH, RET, CALL, etc.
  • If the packer uses SEH, anticipate OEP by tracking stack areas used to store the packers’ handlers.
  • Decode protected data by examining results of the decoding function via dynamic code analysis.
  • Correct PE header problems with XPELister, LordPE, ImpREC, PEiD, etc.
  • To get closer to OEP, try breaking on unpacker’s calls to LoadLibraryA or GetProcAddress.

Common x86 Registers and Uses

EAX Addition, multiplication, function results
ECX Counter
EBP Base for referencing function arguments (EBP+value) and local variables (EBP-value)
ESP Points to the current “top” of the stack; changes via PUSH, POP, and others
EIP Points to the next instruction
EFLAGS Contains flags that store outcomes of computations (e.g., Zero and Carry flags)

Post-Scriptum

If you have suggestions for improving this cheat sheet, please let me know. Creative Commons v3 “Attribution” License for this Cheat Sheet v.1.6. Take a look at my other security cheat sheets.

Updated

About the Author

Lenny is a business and tech leader with extensive experience in information technology and security. His areas of expertise include incident response, cloud services and product management. Lenny focuses on safeguarding customers' IT operations at NCR Corporation. He also teaches digital forensics and anti-malware courses at SANS Institute. Lenny frequently speaks at conferences, 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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