SUMMARY

Specifically-crafted archive and container files can potentially bypass initial malware scans in some products. 

AFFECTED PRODUCTS

ISSUES

Severity

Low

MITIGATION

Details

Symantec received information on various malformed or specifically formatted archive or container files, tar/zip/rar/pdf etc. that have the potential of bypassing scans in some scanning products. Depending on the product doing the initial scanning of the archive or container file, this can sometimes result in files, which haven’t been properly content scanned, reaching client systems. While these modified files many times are corrupted out of any expected format, some applications will still recognize them and attempt to extract or read the content.

Symantec Response

Symantec is well aware of the potential for malicious use of malformed archive/container files. Symantec gateway products detect malformed files, such as a malformed archive or container file, by default. Administrative policy controls exist in Symantec gateway products for these types of malformed files to be blocked or stripped prior to entering the network or quarantined for admin review and actions. Symantec recommends such policy control be used as part of a “defense-in-depth” security policy to restrict potentially harmful content from entering the internal network. 

In the event that these malformed files get through to client/end-user systems, potential malware archived in this manner is not an active threat while it remains archived. However, should known malicious code be delivered to a client system in this manner, Symantec’s Auto Protect or Real Time Virus Scan components would detect malicious content during access attempts as the container or file is opened. 

Should previously unidentified malicious code be distributed in this manner, Symantec’s Security Response is committed to react immediately with updated threat detections via Symantec LiveUpdate or Rapid Release Definitions.

Best Practices

As part of normal best practices, Symantec strongly recommends: 

• Restrict access to administration or management systems to privileged users.
• Restrict remote access, if required, to trusted/authorized systems only.
• Run under the principle of least privilege where possible to limit the impact of exploit by threats.
• Keep all operating systems and applications updated with the latest vendor patches.
• Follow a multi-layered approach to security. Run both firewall and anti-malware applications, at a minimum, to provide multiple points of detection and protection to both inbound and outbound threats.
• Be cautious of unsolicited attachments and executables delivered via email or via instant messaging.
• Do not open email from unknown sources.
• Do not follow links or download content provided by unknown or untrusted sources.
• Email addresses can easily be spoofed so a message appears to come from someone you know. If a message seems suspicious or is unexpected, contact the sender before opening attachments or following web links.

ACKNOWLEDGEMENTS

Symantec would like to thank Thierry Zoller for identifying these malformed formats.