source: http://www.securityfocus.com/bid/17926/info

Microsoft Windows is susceptible to a heap-corruption vulnerability while attempting to read specially crafted CHM or ITS files. This occurs in the 'ITSS.DLL' library.

This vulnerability allows remote attackers to execute arbitrary machine code in the context of applications using the affected library.

Attackers may exploit this issue by coercing users to open malicious CHM or ITS files with Internet Explorer, or when users try to decompile such files using the 'hh -decompile' command. CHM files are considered unsafe files, so there is a possibility that advanced users or security researchers may try to decompile these files to inspect their contents.

https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/bin-sploits/27850.chm