Ubuntu: (CVE-2012-6706): unrar-nonfree vulnerability

A VMSF_DELTA memory corruption was discovered in unrar before 5.5.5, as used in Sophos Anti-Virus Threat Detection Engine before 3.37.2 and other products, that can lead to arbitrary code execution. An integer overflow can be caused in DataSize+CurChannel. The result is a negative value of the "DestPos" variable, which allows the attacker to write out of bounds when setting Mem[DestPos].