chmlib before 0.39 allows user-assisted remote attackers to execute arbitrary code via a crafted page block length in a CHM file, which triggers memory corruption.

CHMLib through 2bef8d0, as used in SumatraPDF and other products, has a chm_lib.c _chm_decompress_block integer overflow. There is a resultant heap-based buffer overflow in _chm_fetch_bytes.