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

Type securityvulns
Reporter Securityvulns
Modified 2011-02-28T00:00:00



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)



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

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

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&gt;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&#40;1&#41;       3.2&#40;2&#41;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&gt; show version
FWSM Firewall Version 3.2&#40;2&#41;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&#40;2&#41;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.


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:

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

  • 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


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 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 by visiting and navigating to Products > Security > Firewall > Firewall Integrated Switch/Router Services > Cisco Catalyst 6500 Series Firewall Services Module > Firewall Services Module (FWSM) Software.


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, or as otherwise set forth at Downloads at

Do not contact or 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

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:

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 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


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.


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

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.


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

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Updated: Feb 23, 2011 Document ID: 112893 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux)