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CERT Advisory CA-2003-13 Multiple Vulnerabilities in Snort
Preprocessors
Original release date: April 17, 2003
Last revised: --
Source: CERT/CC
A complete revision history can be found at the end of this file.
Systems Affected
* Snort IDS, versions 1.8 through 2.0 RC1
Overview
There are two vulnerabilities in the Snort Intrusion Detection
System, each in a separate preprocessor module. Both
vulnerabilities allow remote attackers to execute arbitrary code
with the privileges of the user running Snort, typically root.
I. Description
The Snort intrusion detection system ships with a variety of
preprocessor modules that allow the user to selectively include
additional functionality. Researchers from two independent
organizations have discovered vulnerabilities in two of these modules,
the RPC preprocessor and the "stream4" TCP fragment reassembly
preprocessor.
For additional information regarding Snort, please see
http://www.snort.org/.
VU#139129 - Heap overflow in Snort "stream4" preprocessor
(CAN-2003-0029)
Researchers at CORE Security Technologies have discovered a
remotely exploitable heap overflow in the Snort "stream4"
preprocessor module. This module allows Snort to reassemble
TCP packet fragments for further analysis.
To exploit this vulnerability, an attacker must disrupt the
state tracking mechanism of the preprocessor module by sending a
series of packets with crafted sequence numbers. This causes
the module to bypass a check for buffer overflow attempts and
allows the attacker to insert arbitrary code into the heap.
For additional information, please read the Core Security
Technologies Advisory located at
http://www.coresecurity.com/common/showdoc.php?idx=313&idxseccion=10
This vulnerability affects Snort versions 1.8.x, 1.9.x, and 2.0
prior to RC1. Snort has published an advisory regarding this
vulnerability; it is available at
http://www.snort.org/advisories/snort-2003-04-16-1.txt.
VU#916785 - Buffer overflow in Snort RPC preprocessor
(CAN-2003-0033)
Researchers at Internet Security Systems (ISS) have
discovered a remotely exploitable buffer overflow in the Snort
RPC preprocessor module. Martin Roesch, primary developer for
Snort, described the vulnerability as follows:
When the RPC decoder normalizes fragmented RPC records, it
incorrectly checks the lengths of what is being normalized
against the current packet size, leading to an overflow
condition. The RPC preprocessor is enabled by default.
For additional information, please read the ISS X-Force
advisory located at
http://www.iss.net/issEn/delivery/xforce/alertdetail.jsp?oid=21951
This vulnerability affects Snort versions 1.8.x through 1.9.1
and version 2.0 Beta.
II. Impact
Both VU#139129 and VU#916785 allow remote attackers to
execute arbitrary code with the privileges of the user
running Snort, typically root. In addition, it is not necessary
for the attacker to know the IP address of the Snort device
they wish to attack; merely sending malicious traffic where it
can be observed by an affected Snort sensor is sufficient to
exploit these vulnerabilities.
III. Solution
Upgrade to Snort 2.0
Both VU#139129 and VU#916785 are addressed in Snort version 2.0,
which is available at
http://www.snort.org/dl/snort-2.0.0.tar.gz
Binary-only versions of Snort are available from
http://www.snort.org/dl/binaries
For information from other vendors that ship affected
versions of Snort, please see Appendix A of this document.
Disable affected preprocessor modules
Sites that are unable to immediately upgrade affected Snort
sensors may prevent exploitation of this vulnerability by
commenting out the affected preprocessor modules in the
"snort.conf" configuration file.
To prevent exploitation of VU#139129, comment out the following
line:
preprocessor stream4_reassemble
To prevent exploitation of VU#916785, comment out the following
line:
preprocessor rpc_decode: 111 32771
After commenting out the affected modules, send a SIGHUP signal to the
affected Snort process to update the configuration. Note that
disabling these modules may have adverse affects on a sensor's ability
to correctly process RPC record fragments and TCP packet fragments. In
particular, disabling the "stream4" preprocessor module will prevent
the Snort sensor from detecting a variety of IDS evasion attacks.
Block outbound packets from Snort IDS systems
You may be able limit an attacker's capabilities if the system is
compromised by blocking all outbound traffic from the Snort sensor.
While this workaround will not prevent exploitation of the
vulnerability, it may make it more difficult for the attacker to
create a useful exploit.
Appendix A. - Vendor Information
This appendix contains information provided by vendors for
this advisory. As vendors report new information to the
CERT/CC, we will update this section and note the changes in our
revision history. If a particular vendor is not listed below,
we have not received their comments.
Apple Computer, Inc.
Snort is not shipped with Mac OS X or Mac OS X Server.
Ingrian Networks
Ingrian Networks products are not susceptible to VU#139129
and VU#916785 since they do not use Snort.
Ingrian customers who are using the IDS Extender Service
Engine to mirror cleartext data to a Snort-based IDS should
upgrade their IDS software.
NetBSD
NetBSD does not include snort in the base system.
Snort is available from the 3rd party software system,
pkgsrc. Users who have installed net/snort, net/snort-mysql
or net/snort-pgsql should update to a fixed
version. pkgsrc/security/audit-packages can be used to keep up to
date with these types of issues.
Red Hat Inc.
Not vulnerable. Red Hat does not ship Snort in any of our
supported products.
SGI
SGI does not ship snort as part of IRIX.
Snort
Snort 2.0 has undergone an external third party professional security
audit funded by Sourcefire.
_________________________________________________________________
The CERT/CC acknowledges Bruce Leidl, Juan Pablo Martinez Kuhn, and
Alejandro David Weil of Core Security Technologies for their discovery
of VU#139129. We also acknowledge Mark Dowd and Neel Mehta of ISS
X-Force for their discovery of VU#916785.
_________________________________________________________________
Authors: Jeffrey P. Lanza and Cory F. Cohen.
______________________________________________________________________
This document is available from:
http://www.cert.org/advisories/CA-2003-13.html
______________________________________________________________________
CERT/CC Contact Information
Email: cert@cert.org
Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
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Carnegie Mellon University
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Revision History
April 17, 2003: Initial release
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(99081) /Muhammad Faisal Rauf Danka <mfrd@attitudex.com>/(Ombruten)