An out-of-bounds read vulnerability exists in the way 7-Zip handles Universal Disk Format (UDF) files. The UDF file system was meant to replace the ISO-9660 file format, and was eventually adopted as the official file system for DVD-Video and DVD-Audio.

Central to 7-Zip’s processing of UDF files is the CInArchive::ReadFileItem method. Because volumes can have more than one partition map, their objects are kept in an object vector. To start looking for an item, this method tries to reference the proper object using the partition map’s object vector and the "PartitionRef" field from the Long Allocation Descriptor. Lack of checking whether the "PartitionRef" field is bigger than the available amount of partition map objects causes a read out-of-bounds and can lead, in some circumstances, to arbitrary code execution.

References:

http://blog.talosintel.com/2016/05/multiple-7-zip-vulnerabilities.html