VRT Advisories

VRT Rules 2011-04-27

Sourcefire VRT Rules Update

Date: 2011-04-27


The Sourcefire VRT has identified possible issues with two shared object rules. This release contains modifications to those rules that fix these potential problems.


A problem has been identified in a shared object rule identified as GID 3 SID 18676. This problem causes Snort to hang in an infinite loop when the rule is evaluated.


  1. The set of conditions necessary to cause this rule to enter an infinite loop require a very unique set of content matches to be present in the data being processed. In the unlikely event that these conditions occur, the last content match in the set must not return true.
  2. This set of conditions is very unlikely to occur in normal, non-malicious network traffic.
  3. Additionally, if all the conditions in the rule are met, meaning that a malicious set of traffic was detected, then the rule works as expected and the infinite loop does not occur.
  4. There are currently no known threats available publicly or in the wild for this vulnerability.

Upon review of other custom shared object rule code, a similar issue was found in GID 3, SID 17665. The VRT has pro-actively fixed that rule.

The modifications to GID 3, SIDs 18676 and 17665 are included in this release.

Rule Pack Summary:

For a complete list of new and modified rules, click here.


Sourcefire VRT rule packs often utilize enhancements made to Snort. Operators should upgrade to the latest revision or patch level for Snort to ensure these enhancements are available before using these rules.

About the VRT:

The Sourcefire VRT is a group of leading edge intrusion detection and prevention experts working to proactively discover, assess and respond to the latest trends in hacking activity, intrusion attempts and vulnerabilities. This team is also supported by the vast resources of the open source Snort community, making it the largest group dedicated to advances in the network security industry.

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