The virus detection engine in Sophos Anti-Virus before 2.49.0 does not properly process malformed (1) CAB, (2) LZH, and (3) RAR files with modified headers, which might allow remote attackers to bypass malware detection.
Multiple interpretation error in Sophos 3.91 with the 2.28.4 engine allows remote attackers to bypass virus scanning via a file such as BAT, HTML, and EML with an "MZ" magic byte sequence which is normally associated with EXE, which causes the file to be treated as a safe type that could still be executed as a dangerous file type by applications on the end system, as demonstrated by a "triple headed" program that contains EXE, EML, and HTML content, aka the "magic byte bug."
Sophos Anti-Virus 3.78 allows remote attackers to bypass virus scanning by using a qmail generated Delivery Status Notification (DSN) where the original email is not included in the bounce message.