Cisco Security Advisory: Cisco IOS Software Zone-Based Policy Firewall Vulnerability

23 Sep 2009

Cisco IOS� devices that are configured with Cisco IOS Zone-Based
Policy Firewall Session Initiation Protocol (SIP) inspection are
vulnerable to denial of service (DoS) attacks when processing a
specific SIP transit packet. Exploitation of the vulnerability could
result in a reload of the affected device.

Cisco has released free software updates that address this
vulnerability.

Workarounds that mitigate this vulnerability are available.

This advisory is posted at:

http://www.cisco.com/warp/public/707/cisco-sa-20090923-ios-fw.shtml

Note: The September 23, 2009, Cisco IOS Security Advisory bundled
publication includes eleven Security Advisories. Ten of the
advisories address vulnerabilities in Cisco IOS Software, and one
advisory addresses a vulnerability in Cisco Unified Communications
Manager. Each advisory lists the releases that correct the
vulnerability or vulnerabilities detailed in the advisory. The
following table lists releases that correct all Cisco IOS Software
vulnerabilities that have been published on September 23, 2009, or
earlier.

http://www.cisco.com/warp/public/707/cisco-sa-20090923-bundle.shtml

Individual publication links are in "Cisco Event Response: Semiannual
Cisco IOS Software Advisory Bundled Publication" at the following
link:

http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_sep09.html

Affected Products
=================

This vulnerability affects a limited number of Cisco IOS Software
releases. Consult the "Software Versions and Fixes" section of this
advisory for the details of affected releases.

Only devices that are configured with Cisco IOS Zone-Based Policy
Firewall SIP inspection (UDP port 5060, TCP ports 5060, and 5061) are
vulnerable. Cisco IOS devices that are configured with legacy Cisco
IOS Firewall Support for SIP (context-based access control (CBAC))
are not vulnerable.

Vulnerable Products
+------------------

To determine the Cisco IOS Software release that is running on a
Cisco product, administrators can log in to the device and issue the 
"show version" command to display the system banner. The system banner
confirms that the device is running Cisco IOS Software by displaying
text similar to "Cisco Internetwork Operating System Software" or
"Cisco IOS Software." The image name displays in parentheses,
followed by "Version" and the Cisco IOS Software release name. Other
Cisco devices do not have the "show version" command or may provide
different output.

The following example identifies a Cisco product that is running
Cisco IOS Software Release 12.3(26) with an installed image name of
C2500-IS-L:

    Router#show version
    Cisco Internetwork Operating System Software
    IOS (tm) 2500 Software (C2500-IS-L), Version 12.3(26), RELEASE SOFTWARE (fc2)
    Technical Support: http://www.cisco.com/techsupport
    Copyright �) 1986-2008 by cisco Systems, Inc.
    Compiled Mon 17-Mar-08 14:39 by dchih

    <output truncated>

The following example identifies a Cisco product that is running
Cisco IOS Software Release 12.4(20)T with an installed image name of
C1841-ADVENTERPRISEK9-M:

    Router#show version
    Cisco IOS Software, 1841 Software (C1841-ADVENTERPRISEK9-M), Version 12.4(20)T, RELEASE SOFTWARE (fc3)
    Technical Support: http://www.cisco.com/techsupport
    Copyright �) 1986-2008 by Cisco Systems, Inc.
    Compiled Thu 10-Jul-08 20:25 by prod_rel_team

    <output truncated>

Additional information about Cisco IOS Software release naming
conventions is available in "White Paper: Cisco IOS Reference Guide"
at the following link:

http://www.cisco.com/warp/public/620/1.html

The device is vulnerable if the configuration has either a layer 3 or
layer 7 SIP application-specific policy configured, and these
policies are applied to any firewall zone. To determine whether the
device is running a vulnerable configuration, log in to the device
and issue the command line interface (CLI) command "show policy-map
type inspect zone-pair | include atch: access|protocol sip". If the
output contains "Match: protocol sip", the device is vulnerable. If
the output contains "Match: access-group number", then the device is
only vulnerable "if", the referenced access list permits the SIP
protocol (UDP port 5060, or TCP ports 5060 and 5061). The following
example shows a vulnerable device configured with Cisco IOS
Zone-Based Policy Firewall SIP inspection:

    Router#show policy-map type inspect zone-pair | include atch: access|protocol sip
          Match: protocol sip
    Router#

The following example shows a vulnerable device configured with SIP
inspection by way of an applied access list:

    Router#show policy-map type inspect zone-pair | include atch: access|protocol sip
          Match: access-group 102
    Router#
    Router#show access-list 102
    Extended IP access list 102
        10 permit udp any any eq 5060
        20 permit tcp any any eq 5060
        30 permit tcp any any eq 5061
    Router#

A device that is not configured for SIP inspection or does not
support this configuration will return either a blank line or an
error message. The following is an example of a device that supports
Cisco IOS Firewall but does not have SIP inspection enabled:

    Router#show policy-map type inspect zone-pair | include atch: access|protocol sip
    Router#

Products Confirmed Not Vulnerable
+--------------------------------

No other Cisco products are currently known to be affected by this
vulnerability. Products confirmed not vulnerable include:

  * Cisco PIX 500 Series Firewall
  * Cisco ASA 5500 Series Adaptive Security Appliance
  * Firewall Services Module (FWSM) for Catalyst 6500 Series Switches
    and 7600 Series Routers
  * Virtual Firewall (VFW) application on the multiservice blade
    (MSB) on the Cisco XR 12000 Series Router
  * Cisco ACE Application Control Engine Module
  * Cisco IOS devices NOT configured with Cisco IOS Zone-Based Policy
    Firewall SIP inspection.
  * Cisco IOS devices configured with legacy Cisco IOS Firewall
    Support for SIP (CBAC)
  * Cisco IOS XE Software
  * Cisco IOS XR Software

Details
=======

Firewalls are networking devices that control access to the network
assets of an organization. Firewalls are often positioned at the
entrance points into networks. Cisco IOS software provides a set of
security features that enable you to configure a simple or elaborate
firewall policy, according to your particular requirements.

SIP inspection in the Cisco IOS Firewall provides basic SIP inspect
functionality (SIP packet inspection and pinhole opening) as well as
protocol conformance and application security.

Cisco IOS Software that is configured with Cisco IOS Zone-Based
Policy Firewall SIP inspection are vulnerable to a DoS attack when
processing a specific SIP transit packet. Exploitation of this
vulnerability will result in a reload of the affected device.

Cisco IOS Zone-Based Policy Firewall SIP inspection was first
introduced in Cisco IOS Software versions 12.4(15)XZ and 12.4(20)T.

Cisco IOS Firewall CBAC support for SIP inspection by way of the "ip
inspect name [inspection_name] sip" is not vulnerable. Additional
information regarding Cisco IOS Firewall CBAC support for SIP
inspection is available in the document "Firewall Support for SIP" at
the following link:

http://www.cisco.com/en/US/docs/ios/sec_data_plane/configuration/guide/sec_f...

Additional information regarding Cisco IOS Zone-Based Policy Firewall
SIP inspection is available in the document "Cisco IOS Firewall: SIP
Enhancements: ALG and AIC" at the following link:

http://www.cisco.com/en/US/docs/ios/security/configuration/guide/sec_sip_alg...

This vulnerability is documented in the following Cisco Bug ID: 
CSCsr18691 and has been assigned the Common Vulnerabilities and Exposures
(CVE) identifier CVE-2009-2867.

Vulnerability Scoring Details
=============================

Cisco has provided scores for the vulnerability in this advisory
based on the Common Vulnerability Scoring System (CVSS). The CVSS
scoring in this Security Advisory is done in accordance with CVSS
version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then
compute environmental scores to assist in determining the impact of
the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding
CVSS at:

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at:

http://intellishield.cisco.com/security/alertmanager/cvss

CSCsr18691 - Cisco IOS Software Zone-Based Policy Firewall

CVSS Base Score - 7.8

Access Vector           - Network
Access Complexity       - Low
Authentication          - None
Confidentiality Impact  - None
Integrity Impact        - None
Availability Impact     - Complete

CVSS Temporal Score - 6.4

Exploitability          - Functional
Remediation Level       - Official-Fix
Report Confidence       - Confirmed

Impact
======

Successful exploitation of the vulnerability may result in a reload
of the affected device. Repeated exploit attempts may result in a
sustained DoS attack.

Software Versions and Fixes
===========================

When considering software upgrades, also consult:

http://www.cisco.com/go/psirt

and any subsequent advisories to determine exposure and a complete
upgrade solution.

In all cases, customers should exercise caution to be certain the
devices to be upgraded contain sufficient memory and that current
hardware and software configurations will continue to be supported
properly by the new release. If the information is not clear, contact
the Cisco Technical Assistance Center (TAC) or your contracted
maintenance provider for assistance.

Each row of the Cisco IOS software table (below) names a Cisco IOS
release train. If a given release train is vulnerable, then the
earliest possible releases that contain the fix (along with the
anticipated date of availability for each, if applicable) are listed
in the "First Fixed Release" column of the table. The "Recommended
Release" column indicates the releases which have fixes for all the
published vulnerabilities at the time of this Advisory. A device
running a release in the given train that is earlier than the release
in a specific column (less than the First Fixed Release) is known to
be vulnerable. Cisco recommends upgrading to a release equal to or
later than the release in the "Recommended Releases" column of the
table.

+-------------------------------------------------------------------+
|  Major Release  |        Availability of Repaired Releases        |
|-----------------+-------------------------------------------------|
|    Affected     |                           |                     |
|   12.0-Based    |    First Fixed Release    | Recommended Release |
|    Releases     |                           |                     |
|-------------------------------------------------------------------|
| There are no affected 12.0 based releases                         |
|-------------------------------------------------------------------|
|    Affected     |                           |                     |
|   12.1-Based    |    First Fixed Release    | Recommended Release |
|    Releases     |                           |                     |
|-------------------------------------------------------------------|
| There are no affected 12.1 based releases                         |
|-------------------------------------------------------------------|
|    Affected     |                           |                     |
|   12.2-Based    |    First Fixed Release    | Recommended Release |
|    Releases     |                           |                     |
|-------------------------------------------------------------------|
| There are no affected 12.2 based releases                         |
|-------------------------------------------------------------------|
|    Affected     |                           |                     |
|   12.3-Based    |    First Fixed Release    | Recommended Release |
|    Releases     |                           |                     |
|-------------------------------------------------------------------|
| There are no affected 12.3 based releases                         |
|-------------------------------------------------------------------|
|    Affected     |                           |                     |
|   12.4-Based    |    First Fixed Release    | Recommended Release |
|    Releases     |                           |                     |
|-----------------+---------------------------+---------------------|
| 12.4            | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4GC          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JA          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JDA         | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JDC         | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JDD         | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JK          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JL          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JMA         | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JMB         | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4JX          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4MD          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4MDA         | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4MR          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4SW          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
|                 | Releases prior to 12.4    | 12.4(20)T4          |
|                 | (20)T are not vulnerable; |                     |
|                 |                           | 12.4(22)T3          |
| 12.4T           | 12.4(20)T2                |                     |
|                 |                           | 12.4(24)T2;         |
|                 | 12.4(22)T1                | Available on        |
|                 |                           | 23-OCT-2009         |
|                 | 12.4(24)T                 |                     |
|-----------------+---------------------------+---------------------|
| 12.4XA          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XB          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XC          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XD          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XE          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XF          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XG          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XJ          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XK          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XL          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XM          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XN          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XP          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XQ          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XR          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XT          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XV          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XW          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4XY          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
|                 |                           | 12.4(20)T4          |
|                 |                           |                     |
|                 | Vulnerable; first fixed   | 12.4(22)T3          |
| 12.4XZ          | in 12.4T                  |                     |
|                 |                           | 12.4(24)T2;         |
|                 |                           | Available on        |
|                 |                           | 23-OCT-2009         |
|-----------------+---------------------------+---------------------|
|                 |                           | 12.4(22)T3          |
|                 | Vulnerable; first fixed   |                     |
| 12.4YA          | in 12.4T                  | 12.4(24)T2;         |
|                 |                           | Available on        |
|                 |                           | 23-OCT-2009         |
|-----------------+---------------------------+---------------------|
|                 |                           | 12.4(22)YB4         |
|                 |                           |                     |
| 12.4YB          | 12.4(22)YB4               | 12.4(22)YB5;        |
|                 |                           | Available on        |
|                 |                           | 19-OCT-2009         |
|-----------------+---------------------------+---------------------|
| 12.4YD          | Not Vulnerable            |                     |
|-----------------+---------------------------+---------------------|
| 12.4YE          | Not Vulnerable            |                     |
+-------------------------------------------------------------------+

Workarounds
===========

The only workaround for this vulnerability is to disable Cisco IOS
zone-based policy firewall SIP inspection in the affected device's
configuration. Disabling SIP inspection will allow the rest of the
firewall features to continue to function until a software upgrade
can be implemented. All other firewall features will continue to
perform normally. Disabling SIP Inspection will vary depending on the
implementation of the SIP inspection firewall.

Obtaining Fixed Software
========================

Cisco has released free software updates that address these
vulnerabilities. Prior to deploying software, customers should
consult their maintenance provider or check the software for feature
set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets
they have purchased. By installing, downloading, accessing or
otherwise using such software upgrades, customers agree to be bound
by the terms of Cisco's software license terms found at:

http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html

or as otherwise set forth at Cisco.com Downloads at:

http://www.cisco.com/public/sw-center/sw-usingswc.shtml

Do not contact psirt@cisco.com or security-alert@cisco.com for
software upgrades.

Customers with Service Contracts
+-------------------------------

Customers with contracts should obtain upgraded software through
their regular update channels. For most customers, this means that
upgrades should be obtained through the Software Center on Cisco's
worldwide website at http://www.cisco.com.

Customers using Third Party Support Organizations
+------------------------------------------------

Customers whose Cisco products are provided or maintained through
prior or existing agreements with third-party support organizations,
such as Cisco Partners, authorized resellers, or service providers
should contact that support organization for guidance and assistance
with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific
customer situations, such as product mix, network topology, traffic
behavior, and organizational mission. Due to the variety of affected
products and releases, customers should consult with their service
provider or support organization to ensure any applied workaround or
fix is the most appropriate for use in the intended network before it
is deployed.

Customers without Service Contracts
+----------------------------------

Customers who purchase direct from Cisco but do not hold a Cisco
service contract, and customers who purchase through third-party
vendors but are unsuccessful in obtaining fixed software through
their point of sale should acquire upgrades by contacting the Cisco
Technical Assistance Center (TAC). TAC contacts are as follows.

  * +1 800 553 2447 (toll free from within North America)
  * +1 408 526 7209 (toll call from anywhere in the world)
  * e-mail: tac@cisco.com

Customers should have their product serial number available and be
prepared to give the URL of this notice as evidence of entitlement to
a free upgrade. Free upgrades for non-contract customers must be
requested through the TAC.

Refer to:

http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html

for additional TAC contact information, including localized telephone
numbers, and instructions and e-mail addresses for use in various
languages.

Exploitation and Public Announcements
=====================================

The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerability described in this advisory.

This vulnerability was discovered by Cisco internal testing.

Status of this Notice: FINAL
============================

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY
KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE
INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS
AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS
DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that
omits the distribution URL in the following section is an
uncontrolled copy, and may lack important information or contain
factual errors.

Distribution
============

This advisory is posted on Cisco's worldwide website at :

http://www.cisco.com/warp/public/707/cisco-sa-20090923-ios-fw.shtml

In addition to worldwide web posting, a text version of this notice
is clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients.

  * cust-security-announce@cisco.com
  * first-bulletins@lists.first.org
  * bugtraq@securityfocus.com
  * vulnwatch@vulnwatch.org
  * cisco@spot.colorado.edu
  * cisco-nsp@puck.nether.net
  * full-disclosure@lists.grok.org.uk
  * comp.dcom.sys.cisco@newsgate.cisco.com

Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on
mailing lists or newsgroups. Users concerned about this problem are
encouraged to check the above URL for any updates.

Revision History
================

+----------------------------------------+
| Revision |                   | Initial |
| 1.0      | 2009-September-23 | public  |
|          |                   | release |
+----------------------------------------+

Cisco Security Procedures
=========================

Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and
registering to receive security information from Cisco, is available
on Cisco's worldwide website at:

http://www.cisco.com/en/US/products/products_security_vulnerability_policy.h...

This includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at:

http://www.cisco.com/go/psirt
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Cisco Systems Product Security Incident Response Team

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