Cisco Firewall Services Module Cut-Through Proxy Denial of Service Vulnerability

Summary

• Cisco Firewall Services Module (FWSM) Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a reload of an affected system.
  
  The vulnerability is due to a race condition when releasing the memory allocated by the cut-through proxy function. An attacker could exploit this vulnerability by sending traffic to match the condition that triggers cut-through proxy authentication.
  
  Cisco has released software updates that address this vulnerability. Workarounds that mitigate the vulnerability are not available. This advisory is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20140219-fwsm

Affected Products

• Cisco FWSM Software for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers is affected by this vulnerability. Consult the "Software Versions and Fixes" section of this security advisory for more information about the affected releases.
  
  Cisco FWSM Software has reached the end of software maintenance releases milestone. Cisco FWSM customers are encouraged to contact their Cisco representative for available replacement.

  Vulnerable Products

  Cisco FWSM is affected by this vulnerability if the cut-through proxy function is enabled. This function can be enabled for authentication, authorization and accounting via the match command or include commands. To determine whether this feature is in use, use the show running-config aaa authentication| include match|include command and verify that it returns output. Configurations that use an external AAA server or the Cisco FWSM local user database for AAA are vulnerable.
  
  The following example shows a Cisco FWSM configured to authenticate traffic matching the access list SERVER_AUTH through the external AAA server called AuthOutbound. The configuration in the example is implemented with the match command.
  
  

  FWSM/admin# show running-config aaa authentication| include match|include 
  aaa authentication match SERVER_AUTH inside AuthOutbound
  
  

  The following example shows an equivalent configuration implemented with the include command.
  
  

  FWSM/admin# show running-config aaa authentication| include match|include 
  aaa authentication include SERVER_AUTH inside AuthOutbound

  
  The cut-through proxy function is not enabled by default on Cisco FWSM Software.
  
  

  Determine the Running Software Version

  To determine the version of the Cisco FWSM software that is running on a device, administrators can issue the show version command, as shown in the following example:

  FWSM> show version
  
  FWSM Firewall Version 4.0(16)
  [...]

  
  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 Cisco ASDM window. The version notation is similar to the following example:

  FWSM Version: 4.0(16)

  
  Version information can also be obtained from the Cisco Catalyst 6500 Series Switch or the Cisco 7600 Series Router. To determine the version of Cisco FWSM Software that is running on a device, issue the show module command from Cisco IOS Software or Cisco Catalyst Operating System Software to identify which 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)       8.7(0.22)BUB Ok
    2  0018.ba41.5092 to 0018.ba41.5099   4.0   7.2(1)       4.0(16)      Ok
    3  0014.a90c.9956 to 0014.a90c.995d   5.0   7.2(1)       7.0(4)E4     Ok
    4  0014.a90c.66e6 to 0014.a90c.66ed   1.7   Unknown      Unknown      PwrDown
    5  0013.c42e.7fe0 to 0013.c42e.7fe3   4.4   8.1(3)       12.2(33)SXH8 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)       4.0(16)      Ok
  
  [...]

  
  The preceding example shows that the Cisco FWSM is running software version 4.0(16) as indicated by the Sw column.
  
  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 but will include module information for the modules in each switch in the VSS.

  Products Confirmed Not Vulnerable

  Cisco ASA Software is not affected by this vulnerability.
  
  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.
  
  Cisco FWSM Software supports the cut-through proxy feature for AAA network access services.
  
  A vulnerability in the cut-through proxy function of Cisco Firewall Services Module (FWSM) Software could allow an unauthenticated, remote attacker to cause a reload of the affected system.
  
  

  The vulnerability is due to a race condition when releasing the memory allocated by the cut-through proxy function. An attacker could exploit this vulnerability by sending traffic to match the condition that triggers cut-through proxy authentication. An exploit could allow the attacker to trigger a reload of the affected system. Repeated exploitation could result in a denial of service (DoS) condition.

  
  
  Note: This vulnerability affects both routed and transparent firewall mode in both single and multiple context mode. This vulnerability can be triggered by IP version 4 (IPv4) traffic only. Transit traffic and traffic directed to the FWSM device can be used to trigger this vulnerability. Configurations that use an external AAA server or the Cisco FWSM local user database for AAA vulnerable.
  
  This vulnerability is documented in Cisco bug ID CSCuj16824 (registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2014-0710.

Workarounds

• There are no workarounds that mitigate this vulnerability other than disabling the cut-through proxy feature.

Fixed Software

• When considering software upgrades, customers are advised to consult the Cisco Security Advisories, Responses, and Notices archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.

  In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.

  The following table gives information on the release that fixes this vulnerability for each of the major release versions.
  
  

  	3.1	3.2	4.0	4.1
  CSCuj16824 - Cisco FWSM Cut-Through Proxy Denial of Service Vulnerability1	Migrate to 3.2.x or later	3.2(28)	Migrate to 4.1 or later	4.1(15)

  
  ¹ This vulnerability does not affect Cisco FWSM Software releases prior to 3.1(21), 3.2(21), 4.0(16), and 4.1(6).
  
  Note: Cisco FWSM Software has reached the end of software maintenance releases milestone. Cisco FWSM customers are encouraged to contact their Cisco representative for an available replacement.

Exploitation and Public Announcements

• The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

  This vulnerability was found during the resolution of support cases.

URL

• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20140219-fwsm

Revision History

• Revision 1.0

  2014-February-19

  Initial public release

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