Summary

• 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 3.2(3).

  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 software updates that address this vulnerability.

  A workaround that mitigates this vulnerability is available.

  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071219-fwsm.

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 system.

  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 example.

  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).
    
  • Cisco PIX 500 Series Security Appliance (PIX).
    
  • Cisco 5500 Series Adaptive Security Appliance (ASA).
    

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

Details

• 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 ( registered customers only) .

Workarounds

• 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 two 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
  FWSM(config)#
  FWSM#

  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.

Fixed Software

• When considering software upgrades, 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.

  FWSM software version 3.2(4) contains the fixes for the vulnerability described in this document and will be available for download during the week beginning 7th January 2008.

  FWSM software will be available for download from the following location on cisco.com: http://www.cisco.com/pcgi-bin/tablebuild.pl/cat6000-fwsm?psrtdcat20e2 ( registered customers only) .

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.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071219-fwsm

Revision History

• Revision 1.2	2008-January-3	Updated the download availability date of the Software Versions and Fixes section.
  Revision 1.1	2007-December-19	Updated the temporal score section of the CVSS table.
  Revision 1.0	2007-December-19	Initial public release.

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