CERT Advisory CA-2003-13 Multiple Vulnerabilities in Snort Preprocessors
From: CERT Advisory (firstname.lastname@example.org)
Date: Thu, 17 Apr 2003 11:29:21 -0400 From: CERT Advisory <email@example.com> To: firstname.lastname@example.org
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CERT Advisory CA-2003-13 Multiple Vulnerabilities in Snort Preprocessors
Original release date: April 17, 2003
Last revised: --
A complete revision history can be found at the end of this file.
* Snort IDS, versions 1.8 through 2.0 RC1
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.
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
For additional information regarding Snort, please see
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
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
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
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
This vulnerability affects Snort versions 1.8.x through 1.9.1 and
version 2.0 Beta.
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.
Upgrade to Snort 2.0
Both VU#139129 and VU#916785 are addressed in Snort version 2.0, which
is available at
Binary-only versions of Snort are available from
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:
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
Apple Computer, Inc.
Snort is not shipped with Mac OS X or Mac OS X Server.
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
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
SGI does not ship snort as part of IRIX.
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:
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April 17, 2003: Initial release
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