Public Vulnerability Reports

Multiple Vendor Antivirus RAR File Denial of Service Vulnerability



AntiVirus products typically handle searching files for known viruses within their scan engines. Most scan engines support searching inside of known archive types for viruses as well. For more information refer to any of the popular AntiVirus vendors' web sites.


Remote exploitation of a denial of service vulnerability in Multiple Vendors' Antivirus engines allows an attacker to cause the engines to consume excessive resources.

The affected vendors' scan engines are vulnerable to a DoS attack when scanning malformed RAR archives. Specifically, the malformed archives will have the head_size and pack_size fields set to zero in the Archive Header section. When such a file is encountered, the affected scan engines will enter an infinite loop.


Exploitation allows an attacker to cause the affected scan engine to consume excessive CPU or memory resources. The malicious RAR file would need to be uploaded to a server to initiate the attack. Several common ways this could be achieved include; e-mail attachments, available network shares, FTP accounts, or Web form uploads.

The impact of the vulnerability varies slightly from vendor to vendor as described below.


Scanning of archives is not enabled by default and must be specified by the user. This denial of service attack will prevent the scanner from scanning other files on disk while it is stuck on the exploit file. The hung process can be stopped by the user.

Computer Associates:

This denial of service attack will prevent the scanner from scanning other files on disk while it is stuck on the exploit file. The hung process can be quit by the user and does not consume all system resources.

Trend Micro:

Once attacked, the scan engine will consume 99 percent of CPU resources and the affected computer will require a reboot to recover from the condition. The scan engine process cannot be forced to quit, although its thread priority can be lowered to regain some use of the system before reboot.


iDefense has confirmed this vulnerability exists in the following vendors' products. This should not be considered an exhaustive list as these vendors tend to include the scan engine in many of their products. Previous versions are likely to be affected as well.

  • Sophos Small business edition (Windows/Linux) 4.06.1 with engine version 2.34.3.
  • Computer Associates eTrust Antivirus v7.1.8.0 (A/V engine version 12.4.1)
  • Trend Micro PC Cillin - Internet Security 2006
  • Trend Micro Office Scan 7.3
  • Trend Micro Server Protect 5.58


For Sophos' scan engine, this exploit will not have any effect if the "Enabled scanning of archives" option is not set. iDefense is currently unaware of a workaround for this issue for the remaining vendor's engines.


Sophos has addressed this problem with new versions of their products. See for more information.

Trend Micro stated that this vulnerability does not affect version 8.320 of their Windows scan engine. Additionally, they have released version 8.150 of the HPUX and AIX builds of their scan engine to address this problem in those environments.

Computer Associates has addressed this vulnerability by releasing updates. These updates are available via the products' automatic update features. More information is available within Computer Associates' advisory at the following URL.


The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2006-5645 to this issue. This is a candidate for inclusion in the CVE list (, which standardizes names for security problems.


09/27/2006 Initial vendor notifications
09/27/2006 Initial vendor response - Trend Micro
09/27/2006 Initial vendor response - Computer Associates
09/28/2006 Initial vendor response - Sophos
12/08/2006 Coordinated public disclosure
07/24/2007 Coordinated public disclosure - Computer Associates


This vulnerability was reported by Titon of BastardLabs, Damian Put <,">>, and an anonymous researcher.

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