This indicates an attack attempt to exploit an Integer Underflow vulnerability in Sophos Anti-Virus.
The vulnerability is due to an error when the vulnerable software handles a maliciously crafted RAR file. A remote attacker may be able to exploit this to execute arbitrary code within the context of the application, via a crafted RAR file.
Sophos Anti-Virus for Windows prior to version 10.2.0
Sophos Anti-Virus for Mac prior to version 8.0.8
Sophos Anti-Virus for Linux/UNIX prior to version 9.0.0
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the most recent upgrade or patch from the vendor.