An exploration of the Microsoft Compiled HTML Help (CHM) file format
David Clipsham
Originally developed as a replacement to WinHelp in the late-90’s and still technically readable in a modern Windows system, the Microsoft Compiled HTML Help (CHM) file format is now generally considered to be a potential cybersecurity risk and organizational cybersecurity policies may prevent native execution through Windows.

Alternative CHM readers exist but as they are largely based on reverse-engineering efforts, there may be subtleties to the format that have yet to be revealed and may result in imperfect or failed attempts to read some CHM file instances.

In this lightning talk we take a quick dive into the structure of the CHM file format. We will explore a specific edge-case that prevented correct reading of some instances of the file format through open-source tooling and we will describe how this was corrected for the betterment of all.
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