VRT Advisories


VRT Rules 2005-08-14

Sourcefire VRT Certified Rules Update

Date: 2005-08-15

Update

The Sourcefire Vulnerability Research Team (VRT) is continuing to investigate the Zotob worm and associated Microsoft PnP Vulnerability. The VRT released rules on August 12th, 2005 that detect all attempts to exploit this vulnerability. These rules are identified as sids 3828 through 4125. The Zotob worm will alert on SID 3999. Inline users may wish to set this rule to 'drop' for added protection.

To ensure detection/prevention of all variants of the worm and additional potential attack vectors, the VRT recommends using Snort v2.3.x or higher. This will ensure the latest detection capabilities are being utilized. In addition, Snort v2.3.x uses are advised to make the following configuration change to snort.conf.

Add ports 139 and 445 to the TCP reassembly configuration.

  1. Open the snort.conf file in a text editor
  2. Move to the line containing "preprocessor stream4_reassemble"
  3. Replace the line with the following:
    preprocessor stream4_reassemble: clientonly, ports 21 23 25 53 80 110 111 139 143 445 513 1433
  4. Save the configuration
  5. Restart Snort

This configuration change is required regardless of the rules being used to detect attacks against the PnP vulnerability. Snort users running Snort version 2.4 and later need not make this change unless they have specified ports to reassemble in the snort.conf already. In this case, make sure the ports 139 and 445 are added to the list.

Snort users should note that rules written specifically to detect the currently known variants of Zotob may be evaded with each subsequent variation and will be prone to an increased false positive threshold. The Sourcefire VRT rules use the advanced capabilities of current versions of snort to nullify the evasion attempts of attack vector variants.

Date: 2005-08-14

Update:

The Sourcefire Vulnerability Research Team (VRT) has received reports of a new worm variant, known as Zotob, that makes use of the Plug-and-Play (PnP) vulnerability (MS05-039) to propagate. The worm uses exploit code that targets the PnP issue via port 445 and upon successful exploitation, it then uses ftp to transfer data from the infecting machine. The newly infected machine then becomes an ftp server itself and begins scanning for other vulnerable hosts to infect.

The VRT released rules on August 12th, 2005 that detect all attempts to exploit this vulnerability. These rules are identified as sids 3828 through 4125. The Zotob worm will alert on SID 3999. Inline users may wish to set this rule to 'drop' for added protection.

In addition, a patch for this vulnerability is available at http://www.microsoft.com/technet/security/Bulletin/MS05-039.mspx.

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 network security industry.