Signed Nullsoft Plug-ins – potential Lolbins

April 14, 2019 in Batch Analysis, Clustering, File Formats ZOO, Living off the land, LOLBins, Reusigned Binaries

A couple of years ago I exported ~12K Nullsoft plugins from a large corpora of installers. It was a part of my research on hooking Nullsoft plug-in APIs that I described here.

Today I revisited this old repo, because it crossed my mind that perhaps some of these DLLs were actually signed. And if they are, I thought, then perhaps some of them will tick the box of re-usigned libraries.

To my surprise, I found over 2K signed plug-ins.

Encouraged by these stats, I ran a script to list all the functions exported by these DLLs. Apart from default exports that can be found in the most popular Nullsoft plug-ins, I was able to find tones of other functions.

There are functions for pretty much every occasion:

  • Internet downloads
  • Resource handling
  • Message Boxes
  • Mathematical functions
  • FTP
  • File operations
  • Audio / Video
  • Unicode
  • Network enumeration
  • Process operations
  • Sqlite3
  • Encryption
  • HTML
  • SSH
  • Hooking
  • String operations
  • GDI / UI primitives
  • XML
  • ZIP
  • Zlib
  • and lots more

There are also ‘more refined’ self-descriptive functions e.g. CreateProcessInjected, InjectDll, _DownloadCompleteFile, SilentOpenURLA, KillAllXBrowserProcesses and a variation of KillProcess functions.

Given the variety of exported functions many of these DLLs must be based of source code of popular foss libraries. Why? It’s really hard to believe someone accidentally included all OpenSSL exports in a working Plug-in.

Being so feature-rich one could use these to build unusual code paths that would rely on code callbacks provided by these signed DLLs. In a way similar to ROP, except re-using functional code blocks instead of a single instructions, their small clusters, or trampolines.

Here’s the whole list if you want to have a look.

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