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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
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Revision
History
April 17, 2003: Initial release
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