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 -
* Sourcefire Advisory 2007-02-19 -
* Sourcefire Support Login -
* Sourcefire Snort Release Notes for 2.6.1.3 -
* Snort downloads -
* DCE/RPC Preprocessor -
* IBM Internet Security Systems Protection Advisory -
* CVE-2006-5276 -
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