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Category:   Device (Firewall)  >   Cisco Firewall Services Module Vendors:   Cisco
Cisco Firewall Service Module Application Inspection Bug Lets Remote Users Deny Service
SecurityTracker Alert ID:  1019120
SecurityTracker URL:
CVE Reference:   CVE-2007-5584   (Links to External Site)
Date:  Dec 19 2007
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 3.2(3) only
Description:   A vulnerability was reported in Cisco Firewall Service Module (FWSM). A remote user can cause denial of service conditions.

A remote user can send specially crafted data to trigger a flaw in the Layer 7 Application Inspection process and cause the target device to reload.

Cisco has assigned Cisco bug ID CSCsl08519 to this vulnerability.

Cisco discovered this vulnerability.

Impact:   A remote user can cause the target device to reload.
Solution:   The vendor plans to issue a fixed version (3.2(4)), to be available the week beginning 31st December 2007 at:

The Cisco advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Not specified

Message History:   None.

 Source Message Contents

Subject:  Cisco Security Advisory: Application Inspection Vulnerability in

Hash: SHA1

Cisco Security Advisory: Application Inspection Vulnerability in Cisco
Firewall Services Module

Advisory ID: cisco-sa-20071219-fwsm

Revision 1.0

Last Updated 2007 December 19 1600 UTC (GMT)

For Public Release 2007 December 19 1600 UTC (GMT)


A vulnerability exists in the Cisco Firewall Services Module (FWSM) 
- - - a high-speed, integrated firewall module for Cisco Catalyst 6500 
switches and Cisco 7600 Series routers,  that may result in a reload
of the FWSM.  The only affected FWSM System Software Version is 

There are no known instances of intentional exploitation of this 
issue. However, Cisco has observed data streams that appear to be
unintentionally triggering this vulnerability.

Common Vulnerabilities and Exposures (CVE) identifier CVE-2007-5584
has been assigned to this vulnerability.

Cisco will release free software updates that address this 

A workaround that mitigates this vulnerability is available.

This advisory is posted at

Affected Products

Vulnerable Products

The FWSM is vulnerable if running System Software version 3.2(3).

To determine if the FWSM is vulnerable, issue the "show module" 
command-line interface (CLI) command from Cisco IOS or Cisco CatOS
to identify what modules and sub-modules are installed in the 

The following example shows a system with a Firewall Service Module 
(WS-SVC-FWM-1) installed in slot 4.

switch#show module
 Mod Ports Card Type                              Model              Serial No.
 --- ----- -------------------------------------- ----------------- -----------
 1   48    SFM-capable 48 port 10/100/1000mb RJ45 WS-X6548-GE-TX    SAxxxxxxxxx
 4    6    Firewall Module                        WS-SVC-FWM-1      SAxxxxxxxxx
 5    2    Supervisor Engine 720 (Active)         WS-SUP720-BASE    SAxxxxxxxxx
 6    2    Supervisor Engine 720 (Hot)            WS-SUP720-BASE    SAxxxxxxxxx

After locating the correct slot, issue the show module <slot number> 
command to identify the software version that is running.

switch#show module 4
 Mod Ports Card Type                              Model              Serial No.
 --- ----- -------------------------------------- ----------------- -----------
 4    6    Firewall Module                        WS-SVC-FWM-1      SAxxxxxxxxx

 Mod MAC addresses                     Hw     Fw           Sw           Status
 --- --------------------------------- ------ ------------ ------------ -------
 4   0003.e4xx.xxxx to 0003.e4xx.xxxx  3.0    7.2(1)       3.2(3)       Ok

The preceding example shows that the FWSM is running version 3.2(3)
as indicated by the column under "Sw" above.

Note: Recent versions of Cisco IOS 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.

Alternatively, the information can also be obtained directly from the
FWSM through the show version command as seen in the following

  FWSM#show version
  FWSM Firewall Version 3.2(3)

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(3)

Products Confirmed Not Vulnerable

  * FWSM System Software versions 3.2(2) and earlier.
  * FWSM System Software versions 3.1(x).
  * FWSM System Software versions 1.x(y) and 2.x(y).
  * The Cisco PIX 500 Series Security Appliance (PIX)
  * The Cisco 5500 Series Adaptive Security Appliance (ASA).

No other Cisco products are currently known to be affected by this


A vulnerability exists in the processing of data in the 
control-plane path with Layer 7 Application Inspections, that may
result in a reload of the FWSM. The vulnerability can be triggered
with standard network traffic, which is passed through the
Application Layer Protocol Inspection process.

The only FWSM release affected by this vulnerability is FWSM System
Software version 3.2(3). 

This vulnerability is documented in Cisco bug ID CSCsl08519.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerabilities 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:

CSCsl08519 - FWSM Version 3.2.3 System Software may crash with
             Application Layer Protocol Inspection                                                                               
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 the vulnerability may result in a reload of
the FWSM.  Repeated exploitation will result in a sustained denial of
service attack.

Software Versions and Fixes

When considering software upgrades, 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.

FWSM software version 3.2(4) contains the fixes for the vulnerability
described in this document and will be available for download the week
beginning 31st December 2007.

FWSM software will be available for download from the following
location on


* Disable the TCP normalizing function
  Disabling the TCP normalizing function in the FWSM will mitigate
  this vulnerability.

  The TCP normalizer performs the following action: for traffic that
  passes through the control-plane path, such as packets that require
  Layer 7 inspection or management traffic, the FWSM sets the maximum
  number of out-of-order packets that can be queued for a TCP
  connection to 2 packets. The TCP normalizer is enabled by default
  and is not configurable except to enable or disable.

  To disable the TCP normalizing function, use the 
  "no control-point tcp-normalizer" command in global configuration
  mode, as shown in the following example.

  FWSM# config terminal
  FWSM(config)# no control-point tcp-normalizer

  Disabling the "control-point tcp-normalizer" will prevent strict
  TCP checks, such as detecting out-of-sequence segments and
  monitoring TCP options, on the TCP packets received on the Control
  Plane for Layer 7 inspection in the FWSM, will not be performed.
  The feature should be re-enabled after upgrading to a fixed version
  of software.

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
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 

Exploitation and Public Announcements

This issue was first discovered via internal testing at Cisco.  There
are no known instances of intentional exploitation of this issue. 
However, Cisco has observed data streams that appear to be
unintentionally triggering the vulnerability.

Status of This Notice: INTERIM


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 | 2007-DECEMBER-19 | 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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