There is a heap based buffer overflow in the rendering engine of .hlp files in winhlp32.exe which will allow some attacker the possibility of modifying the internal structure of the process with a means to execute arbitrary and malicious code.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/45107/windowsHelp.txt
Source: https://packetstormsecurity.com/files/45107/windowsHelp.txt.html