The ENSURE_BITS macro in mszipd.c for Clam AntiVirus (ClamAV) 0.83, and other versions vefore 0.86, allows remote attackers to cause a denial of service (CPU consumption by infinite loop) via a cabinet (CAB) file with the cffile_FolderOffset field set to 0xff, which causes a zero-length read.
http://www.idefense.com/application/poi/display?id=275&type=vulnerabilities