shadow – Firefox Heap Exploitation Tool (jemalloc)

shadow is a new, extended (and renamed version) of a Firefox heap exploitation tool, which is quite a swiss army knife for Firefox/jemalloc heap exploitation.

If you want to dive in really deep to this tool, and the technicalities behind it check this out – OR’LYEH? The Shadow over Firefox [PDF]


shadow has been tested with the following:

  • Windows 8.1 x86-64
  • Windows 7 SP1 x86 and x86-64
  • WinDBG 6.3.9600.17200 x86 (since Firefox stable is x86-only currently)
  • pykd version
  • Many different Firefox releases, but extensively with: 31.7.0-esr, 35.0.1, 36.0.1, 38.0.5, 39.0, 40.0, 43.0. 44.0.


When you issue a jemalloc-specific command for the first time, shadow parses all jemalloc metadata it knows about and saves them to a Python pickle file. Subsequent commands use this pickle file instead of parsing the metadata from memory again in order to be faster.

When you know that the state of jemalloc metadata has changed (for example when you have made some allocations or have triggered a garbage collection), use the jeparse command to re-parse the
metadata and re-create the pickle file.

Symbol Support

The symbol command allows you to search for SpiderMonkey and DOM classes (and structures) of specific sizes. This is useful when you’re trying to exploit use-after-free bugs, or when you want to position interesting victim objects to overwrite/corrupt.

In the “auxiliary” directory you can find a small PDB parsing utility named symhex. Run it on “xul.pdb” to generate the Python pickle file that shadow expects in the “pdb” directory (as “pdb/xul-VERSION.pdb.pkl”). Before running symhex make sure you have registered “msdia90.dll”.

You can download shadow here:

Or read more here.

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