Sourcefire VRT Update for Zotob Worm

[Nigel Houghton <nigel () sourcefire com>]

Sourcefire VRT Update for Zotob Worm

Update: 2005-08-15

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
v2.3.3 or higher. This will ensure the latest detection capabilities are
being utilized. In addition, Snort v2.3.3 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 (ensure it is all on one line):
   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.

+--------------------------------------------------------------------+
     Nigel Houghton      Research Engineer       Sourcefire Inc.
                   Vulnerability Research Team


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