[Full-Disclosure] Fwd: CERT Advisory CA-2003-13 Multiple Vulnerabilities in Snort Preprocessors

From: Muhammad Faisal Rauf Danka (mfrd@attitudex.com)
Date: 04/17/03

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    From: Muhammad Faisal Rauf Danka <mfrd@attitudex.com>
    To: bugtraq@securityfocus.com, full-disclosure@lists.netsys.com
    Date: Thu, 17 Apr 2003 11:17:10 -0700 (PDT)

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    Muhammad Faisal Rauf Danka

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    Date: Thu, 17 Apr 2003 11:30:25 -0400
    From: CERT Advisory <cert-advisory@cert.org>
    To: cert-advisory@cert.org


    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


       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

       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
       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


       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
       located at


       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


       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:

         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

    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


       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:

    CERT/CC Contact Information

       Email: cert@cert.org
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              Carnegie Mellon University
              Pittsburgh PA 15213-3890

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       Revision History
    April 17, 2003: Initial release

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