• Medium (Author)
  • Medium (Specki)


  • Many anti-debugging checks. Probably hard to circumvent
  • Ghidra does not like DotNet Binaries by default. Disassembly is practically unusable

Rabbit Holes:

  • .GetILAsByteArray() returns different values when copy&pasted into seperate program
    • Dependent on internal Method Name Tables? --> Those change based on what the compiler likes most during compiling
    • Trying to recreate the exact assembly feels impossible. Even when copy&pasting the exact codelines, assembly still reorders stuff (Several hours used on this)
    • When reordering functions in Code and compiling values from GetILAsByteArray differ only slightly (+- 5) and differ only on fixed positions (7 total)
      • Bruteforcing the -15 to +15 range of possible values on all 7 locations does not yield correct key and takes a loong time (w/o optimization)
  • Loading the dll into a seperate program is not trivial and requires more C# knowledge
  • Debugging dynamically loaded functions is apparently not possible? Breakpoints are skipped


  • Decompile in dnSpy
  • Find initialCheck function that validates args (used for reme_1). Ignore for now
  • Observations:
    • ilAsByteArray created based on Method body from initialCheck using GetILAsByteArray and is used as AES decryption key later on
      • GetILAsByteArray returns exact raw assembly bytes from the function, result can be extracted using ByteViewer (e.g. inside Ghidra)
    • Memory is searched for hardcoded String THIS_IS_CSCG_NOT_A_MALWARE. All Memory after this string is then decrypted
    • Decrypted Data is loaded dynamically and "Check" is called
  • In Hex Editor String THIS_IS_CSCG_NOT_A_MALWARE can be found near the end of the assembly. Entropy graph suggests all data after this string is encrypted
    • Data can simply be copy-pasted into seperate file encoded_function to be easily accessible
  • AES_Decrypt can be copy&pasted into seperate program and run on extracted key (bytes from initialCheck Function) and encoded_function.
  • In original program flow this assembly was dynamically loaded and Check function called on it
    • Debugging of this dynamically loaded function seems difficult - Breakpoints are ignored
    • Observation: decoded_flag_check starts with bytes 4D 5A 90 00 and includes String "DOS" --> DOS MZ executable format
  • Save decrypted data into new file tmp.exe
    • can be run and provides
  • Decompile tmp.exe via dnSpy. Copy Disassembled Function Check into decrypted_check.txt
  • Analyze Check Function. It compares input against hardcoded constants
    • md5 has can easily be looked up in online md5 databases
    • other constants are human-readable and can be extracted by hand
  • WIN




  • Do not use program text as encryption key
  • Security through obscurity (aka obfuscation) is generally a bad idea