Auditing zlib

TrustInSoft analysis of zlib, finding subtle issues

Auditing zlib

TrustInSoft automated lib audit

zlib is a venerable multi-purpose compression library, first released in May 1995. The first time I installed GNU/Linux was in late 1995, so to me zlib has somehow always existed. Although now that I think about it, the zlib source code was distributed in the Unix compress format: had I been just a little bit more perceptive, I might have inferred that zlib had not existed forever, as a consequence of something else having come before it.


Together with New York based company Trail of Bits and under the auspices of Mozilla’s Secure Open Source program, TrustInSoft has completed an automated audit of zlib. Subtle issues were found, and fixed by zlib co-author Mark Adler.


Dan Guido makes a great argument for taking advantage of all that software tools can offer for auditing software. One of the tools used in this audit is tis-interpreter, to identify C undefined behaviors along the execution traces generated by Trail of Bits’s CRS.


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