Playing with Program database paths…

Many executables include references (typically in a form of .pdb file name) to a program database path used by the software. This path typically points to some location on the software author’s system. I actually tried to cluster these paths in the past to build a list of account names used by malware authors. Of course, today it’s much harder – many modern malware authors randomize this path so it can evade signatures/yara rules.

These paths are used only by programs that actually… use them – primarily debuggers. It is a limitation, but it crossed my mind that we could still try to modify a PDB path to point it to any file really.

After test change and loading the program into Olly debugger I immediately saw that it tries to read the file from various locations. Interestingly, Olly tries to locate the pdb file based on a file name first. It looks for it in a debuggee’s current directory, then in ‘.\exe’ subdirectory, then ‘.\symbols\exe’, then comes back to the current directory and checks the same file name, but with a ‘.pdb’ extension, and finally in the fullpath provided inside the debug section:

This is interesting.

My first thought was to try to DoS Olly by making a reference to c:\pagefile.sys. This didn’t work, because Olly only reads a chunk at the top of the file, then bails out when the file is not present/proper. Also, it doesn’t seem to ‘see’ files with hidden/system attributes.

Another option I looked at was to point it to a file that could be e.g. including EICAR string. Any program reading such file will most likely trigger AV detection – as such killing and quarantining the debugger – – this could act as a truly naive anti-debug technique. Of course, such decoy EICAR file needs to exist first, so program would need to create it after first run. In such case tho, AV would pick the program instead! A perfect catch 22.

Then I thought of another option: we could use it as a beacon. This actually seemed to work pretty fine:

– I could see the request going out to the specified IP:

This could affect not only debuggers, but also any vendor tools that load files and leverage these debug sections by default (e.g. any sort of more advanced automation). As a result, it could flag attackers that the file is ‘burnt’, or the red team’s activity got discovered.

The chances for it being really practically useful are pretty low, but again, there maybe other ideas on how to leverage it that I have not thought of.

After writing this post, one more idea came to my mind – this could be a neat trick against CTF participants.

Anyone ‘caught’ to be using debugger in an online environment could be rickrolled, or put on a ‘harder’ track as a punishment for doing analysis w/o precaution. And of course, a cleverly designed .pdb delivered if analysis was made online could actually throw analysts off as well (e.g. by creating labels in program that could mislead / confuse disassemblers/debuggers).

…and the most popular windows account for compiling malware is:


Many malware samples contain debug strings that include paths often directly pointing to a location where the source code is stored and so it happens that often it’s also a location under the USERPROFILE. For the fun of it, I extracted the strings from a large batch of samples and came up with the following statistics (showing top 50):

   3893 Administrator
   2963 JUANJO
   1121 ryanch
    928 Boy
    617 UserXP
    612 user
    519 1337
    502 User
    465 Admin
    435 root
    422 bld4act
    418 Owner
    347 nosferatus
    305 Administrateur
    300 M4x
    296 ismael
    277 goga
    277 Kyle
    255 Mirko
    247 1134
    244 kdglkrkjdfhslej
    241 FEDERIKO
    234 t0fx
    231 rstephens
    219 DarkCoderSc
    218 gcc
    205 icyheart
    200 Dave
    197 michael
    197 Roshan
    197 James
    195 Ben
    182 John
    178 admin
    173 Dev
    161 box1
    157 nonadmin
    153 FELIPE
    152 Familie
    151 Timothy
    137 Dhivin
    133 Vortex
    131 Robert
    130 dabdoub
    129 USER
    127 dr zinou
    125 packar
    122 David
    116 nathu
    116 Daniel

It’s obviously biased.

Other interesting names include:

  • tom age five
  • Krusty the Clown
  • ^_^
  • ItchyFingerz
  • irishboy
  • romantic
  • lol
  • brad pitt
  • Love Bebe
  • LorD^^$$steal3R
  • Cyber-Warrior Ender
  • auchan
  • F-B-I
  • Valued Sony Customer
  • SexyReplay
  • Microsoft
  • Poo
  • Trojan
  • P@wn3d
  • Emperor Zhou Tai Nu

There are over 7000 account names on the list. If you want the full list, please contact me offline.