TUCoPS :: Unix :: General :: bt9.txt

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年04月16日-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.
 ______________________________________________________________________
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 http://www.cert.org/advisories/CA-2003-13.html
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 Revision History
April 17, 2003: Initial release