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avast! Anti-Virus Engine Malformed ZIP/CAB Archive Virus Detection Bypass Advisory Available in Danish 

Secunia Advisory: SA17126  
Release Date: 2005-10-13

Critical:
Not critical
Impact: Security Bypass
Where: From remote
Solution Status: Unpatched

Software:avast! for Kerio 4.x

This advisory is currently marked as unpatched!
- Companies can be alerted when a patch is released!


Description:
fRoGGz has discovered a weakness in avast! Anti-Virus scan engine, which can be exploited by malware to bypass certain scanning functionality.

The weakness is caused due to an error in parsing certain malformed archives and can be exploited via a specially crafted archive with additional characters prepended to the header. Such malformed archives can be correctly extracted by some archiving software.

Successful exploitation allows malware packed in malformed archives to pass the email anti-virus scanning gateway undetected.

The weakness has been confirmed in avast! for Kerio version 4.6.313 (Vps 0541-1) when scanning an email containing malformed ".zip" and ".cab" archives. Other versions may also be affected.

NOTE: This is not an issue on client systems, as the malware is still detected upon execution by the desktop on-access scanner.

Solution:
Desktop on-access scanner should be used to ensure that the malware is detected upon extraction.

Filter all compressed file archives at border gateways if they are not required.

Provided and/or discovered by:
fRoGGz, SecuBox Labs

Original Advisory:
http://shadock.net/secubox/AVCraftedArchive.html



Please note: The information that this Secunia Advisory is based on comes from a third party unless stated otherwise.

Secunia collects, validates, and verifies all vulnerability reports issued by security research groups, vendors, and others.


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