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Cisco Security Advisory: Cisco Firewall Services Module Skinny Client Control Protocol Inspection Denial of Service Vulnerability



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Cisco Security Advisory: Cisco Firewall Services Module Skinny Client
Control Protocol Inspection Denial of Service Vulnerability

Document ID: 112893

Advisory ID: cisco-sa-20110223-fwsm

Revision 1.0

For Public Release 2011 February 23 1600 UTC (GMT)

+---------------------------------------------------------------------

Summary
=======

A vulnerability exists in the Cisco Firewall Services Module (FWSM)
for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers
that may cause the Cisco FWSM to reload after processing a malformed
Skinny Client Control Protocol (SCCP) message. Devices are affected
when SCCP inspection is enabled.

Cisco has released free software updates that address this
vulnerability.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20110223-fwsm.shtml.

Note: Cisco ASA 5500 Series Adaptive Security Appliances are
affected by the vulnerability described in this advisory. A
separate Cisco Security Advisory has been published to disclose
this and other vulnerabilities that affect the Cisco ASA 5500
Series Adaptive Security Appliances. The advisory is available at
http://www.cisco.com/warp/public/707/cisco-sa-20110223-asa.shtml.

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

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

Versions 3.1.x, 3.2.x, 4.0.x, and 4.1.x of Cisco FWSM software are
affected by this vulnerability if SCCP inspection is enabled. SCCP
inspection is enabled by default.

To determine whether SCCP inspection is enabled, issue the "show
service-policy | include skinny" command and confirm that the command
returns output. Example output follows:

    fwsm#show service-policy | include skinny
          Inspect: skinny , packet 0, drop 0, reset-drop 0

Alternatively, a device that has SCCP inspection enabled has a
configuration similar to the following:

    class-map inspection_default
     match default-inspection-traffic
    !
    policy-map global_policy
     class inspection_default
      ...
      inspect skinny
      ...
    !
    service-policy global_policy global

Note: The service policy could also be applied to a specific
interface. (Global application is shown in the previous example.)

To determine the version of Cisco FWSM software that is running, issue
the "show module" command from Cisco IOS Software or Cisco Catalyst
Operating System Software to identify what modules and submodules are
installed on the system.

The following example shows a system with a Cisco FWSM (WS-SVC-FWM-1)
installed in slot 2:

    switch>show module
    Mod Ports Card Type                              Model              Serial No.
    --- ----- -------------------------------------- ------------------ -----------
      1   16  SFM-capable 16 port 1000mb GBIC        WS-X6516-GBIC      SAL06334NS9
      2    6  Firewall Module                        WS-SVC-FWM-1       SAD10360485
      3    8  Intrusion Detection System             WS-SVC-IDSM-2      SAD0932089Z
      4    4  SLB Application Processor Complex      WS-X6066-SLB-APC   SAD093004BD
      5    2  Supervisor Engine 720 (Active)         WS-SUP720-3B       SAL0934888E

    Mod MAC addresses                       Hw    Fw           Sw           Status
    --- ---------------------------------- ------ ------------ ------------ -------
      1  0009.11e3.ade8 to 0009.11e3.adf7   5.1   6.3(1)       8.5(0.46)RFW Ok
      2  0018.ba41.5092 to 0018.ba41.5099   4.0   7.2(1)       3.2(2)10     Ok
      3  0014.a90c.9956 to 0014.a90c.995d   5.0   7.2(1)       5.1(6)E1     Ok
      4  0014.a90c.66e6 to 0014.a90c.66ed   1.7                4.2(3)       Ok
      5  0013.c42e.7fe0 to 0013.c42e.7fe3   4.4   8.1(3)       12.2(18)SXF1 Ok

    [...]

After locating the correct slot, issue the "show module <slot number>"
command to identify the software version that is running, as shown in
the following example:

    switch>show module 2
    Mod Ports Card Type                              Model              Serial No.
    --- ----- -------------------------------------- ------------------ -----------
      2    6  Firewall Module                        WS-SVC-FWM-1       SAD10360485

    Mod MAC addresses                       Hw    Fw           Sw           Status
    --- ---------------------------------- ------ ------------ ------------ -------
      2  0018.ba41.5092 to 0018.ba41.5099   4.0   7.2(1)       3.2(2)10     Ok

    [...]

The preceding example shows that the FWSM is running software version
3.2(2)10 as indicated by the Sw column.

Note: Recent versions of Cisco IOS Software will show the software
version of each module in the output from the "show module" command;
therefore, executing the "show module <slot number>" command is not
necessary.

If a Virtual Switching System (VSS) is used to allow two physical Cisco
Catalyst 6500 Series Switches to operate as a single logical virtual
switch, the "show module switch all" command can display the software
version of all FWSMs that belong to switch 1 and switch 2. The output
from this command will be similar to the output from "show module <slot
number>" but will include module information for the modules in each
switch in the VSS.

Alternatively, version information can be obtained directly from the
FWSM through the "show version" command, as shown in the following
example:

    FWSM> show version
    FWSM Firewall Version 3.2(2)10
    [...]

Customers who use the Cisco Adaptive Security Device Manager (ASDM)
to manage their devices can find the version of the software
displayed in the table in the login window or in the upper left
corner of the ASDM window. The version notation is similar to the
following example:

    FWSM Version: 3.2(2)10

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

With the exception of Cisco ASA 5500 Series Adaptive Security
Appliances, no other Cisco products are currently known to be
affected by this vulnerability.

Details
=======

The Cisco FWSM is a high-speed, integrated firewall module for Cisco
Catalyst 6500 Series Switches and Cisco 7600 Series Routers. The FWSM
offers firewall services with stateful packet filtering and deep
packet inspection.

The Cisco FWSM is affected by a vulnerability that may cause the
device to reload during the processing of a malformed SCCP message
when SCCP inspection is enabled.

This vulnerability is triggered only by transit traffic; traffic that
is destined to the device does not trigger this vulnerability.

This vulnerability is documented in Cisco bug ID CSCtl84952 and has been
assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2011-0394.

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

* CSCtl84952 ("SCCP inspection DoS vulnerability")

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 this vulnerability may cause a reload of
the affected device. Repeated exploitation could result in a
sustained denial of service condition.

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 following Cisco FWSM software table describes a major
Cisco FWSM software train and the earliest possible release in that
train that contains the fix (the "First Fixed Release") and the
anticipated date of availability (if not currently available) in the
First Fixed Release column. A device that is running a release that
is earlier than the release in a specific column (earlier than the
First Fixed Release) is known to be vulnerable. The release should be
upgraded at least to the indicated release or a later version (later
than or equal to the First Fixed Release label).

+------------------------------------------------------------+
|     Major Release      |        First Fixed Release        |
|------------------------+-----------------------------------|
| 3.1                    | 3.1(20)                           |
|------------------------+-----------------------------------|
| 3.2                    | 3.2(20)                           |
|------------------------+-----------------------------------|
| 4.0                    | 4.0(15)                           |
|------------------------+-----------------------------------|
| 4.1                    | 4.1(5)                            |
+------------------------------------------------------------+

Fixed Cisco FWSM software can be downloaded from the Software Center on
Cisco.com by visiting http://www.cisco.com/cisco/software/navigator.html
and navigating to Products > Security > Firewall > Firewall Integrated
Switch/Router Services > Cisco Catalyst 6500 Series Firewall Services
Module > Firewall Services Module (FWSM) Software.

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

If SCCP inspection is not required, it can be disabled so the device
is no longer affected by the vulnerability. Administrators can
disable SCCP inspection by issuing the "no inspect skinny" command in
class configuration submode in the policy map configuration. If SCCP
inspection is required, there are no workarounds.

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

Cisco has released free software updates that address this
vulnerability. 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@xxxxxxxxx or security-alert@xxxxxxxxx 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@xxxxxxxxx

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 found during 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-20110223-fwsm.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@xxxxxxxxx
  * first-bulletins@xxxxxxxxxxxxxxx
  * bugtraq@xxxxxxxxxxxxxxxxx
  * vulnwatch@xxxxxxxxxxxxx
  * cisco@xxxxxxxxxxxxxxxxx
  * cisco-nsp@xxxxxxxxxxxxxxx
  * full-disclosure@xxxxxxxxxxxxxxxxx
  * comp.dcom.sys.cisco@xxxxxxxxxxxxxxxxxx

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 1.0 | 2011-February-23 | Initial 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.html.
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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Copyright 2010-2011 Cisco Systems, Inc. All rights reserved.
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Updated: Feb 23, 2011                             Document ID: 112893
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