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                     National Cyber Alert System

               Technical Cyber Security Alert TA07-050A


Sourcefire Snort DCE/RPC Preprocessor Buffer Overflow

   Original release date: February 19, 2007
   Last revised: --
   Source: US-CERT


Systems Affected

     * Snort 2.6.1, 2.6.1.1, and 2.6.1.2
     * Snort 2.7.0 beta 1
     * Sourcefire Intrusion Sensors version 4.1.x, 4.5.x, and 4.6x with
       SEUs prior to SEU 64
     * Sourcefire Intrusion Sensors for Crossbeam version 4.1.x, 4.5.x,
       and 4.6x with SEUs prior to SEU 64

   Other products that use Snort or Snort components may be affected.


Overview

   A stack buffer overflow vulnerability in the Sourcefire Snort
   DCE/RPC preprocessor could allow an unauthenticated, remote
   attacker to execute arbitrary code with the privileges of the Snort
   process.


I. Description

   Sourcefire Snort is a widely-deployed, open-source network
   intrusion detection system (IDS). Snort and its components are used
   in other IDS products, notably Sourcefire, and Snort is included
   with a number of operating system distributions. The DCE/RPC
   preprocessor reassembles fragmented SMB and DCE/RPC traffic before
   passing data to the Snort rules.

   The vulnerable code does not properly reassemble certain types of
   SMB and DCE/RPC packets. An attacker could exploit this
   vulnerability by sending a specially crafted TCP packet to a host
   or network monitored by Snort. The DCE/RPC preprocessor is enabled
   by default, and it is not necessary for an attacker to complete a
   TCP handshake.

   US-CERT is tracking this vulnerability as VU#196240. This
   vulnerability has been assigned CVE number CVE-2006-5276. Further
   information is available in advisories from Sourcefire and ISS.


II. Impact

   A remote, unauthenticated attacker may be able to execute arbitrary
   code with the privilege level of the Snort preprocessor.


III. Solution

Upgrade

   Snort 2.6.1.3 is available from the Snort download site. Sourcefire
   customers should visit the Sourcefire Support Login site.

Disable the DCE/RPC Preprocessor

   To disable the DCE/RPC preprocessor, comment out the line that loads
   the preprocessor in the Snort configuration file (typically
   /etc/snort.conf on UNIX and Linux systems):

     [/etc/snort.conf]
     ...
     #preprocessor dcerpc...
     ...
   
   Restart Snort for the change to take effect.

   Disabling the preprocessor will prevent Snort from reassembling
   fragmented SMB and DCE/RPC packets. This may allow attacks to evade
   the IDS.


IV. References

     * US-CERT Vulnerability Note VU#196240 -
       <http://www.kb.cert.org/vuls/id/196240>

     * Sourcefire Advisory 2007-02-19 -
       <http://www.snort.org/docs/advisory-2007-02-19.html>

     * Sourcefire Support Login - <https://support.sourcefire.com/>

     * Sourcefire Snort Release Notes for 2.6.1.3 -
       <http://www.snort.org/docs/release_notes/release_notes_2613.txt>

     * Snort downloads - <http://www.snort.org/dl/>

     * DCE/RPC Preprocessor -
       <http://www.snort.org/docs/snort_htmanuals/htmanual_261/node104.html>

     * IBM Internet Security Systems Protection Advisory -
       <http://iss.net/threats/257.html>

     * CVE-2006-5276 -
       <http://cve.mitre.org/cgi-bin/cvename.cgi?name=cve-2006-5276>


 ____________________________________________________________________

   The most recent version of this document can be found at:

     <http://www.us-cert.gov/cas/techalerts/TA07-050A.html>
 ____________________________________________________________________

   Feedback can be directed to US-CERT Technical Staff. Please send
   email to <cert@cert.org> with "TA07-050A Feedback VU#196240" in the
   subject.
 ____________________________________________________________________

   For instructions on subscribing to or unsubscribing from this
   mailing list, visit <http://www.us-cert.gov/cas/signup.html>.
 ____________________________________________________________________

   Produced 2007 by US-CERT, a government organization.

   Terms of use:

     <http://www.us-cert.gov/legal.html>
 ____________________________________________________________________


Revision History

   February 19, 2007:  Initial Release

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