Summary

• A vulnerability in the proxy cache functionality of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition because the device runs out of system memory.
  
  The vulnerability is due to improper memory operations by the affected software. The software fails to free a memory object when it retrieves data from the proxy server cache to terminate a TCP connection. An attacker could exploit this vulnerability by opening many proxy connections through the WSA. An exploit could allow the attacker to cause the WSA to stop passing traffic when enough memory is leaked.
  
  Cisco has released software updates that address this vulnerability. A workaround that mitigates this vulnerability is also available.
  
  This advisory is available at the following link:
  
  http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151104-wsa1

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco AsyncOS Software versions 8.0 through 8.8 for Cisco WSA on both virtual and hardware appliances.
  

  To determine whether a vulnerable version of Cisco AsyncOS Software is running on a Cisco WSA, administrators can use the version command in the WSA CLI. The following example shows the results for an appliance running Cisco AsyncOS Software version 8.5.3-051:

  ciscowsa> version
  Current Version
  ===============
  Product: Cisco IronPort S670 Web Security Appliance
  Model: S670
  Version: 8.5.3-051
  .
  .
  .

  
  
  See the "Fixed Software" section of this security advisory for more information about the affected versions.

  Products Confirmed Not Vulnerable

  The following products are not affected by this vulnerability:
  

  • Cisco Email Security Appliance (ESA), both virtual and hardware versions
  • Cisco Security Mail Appliance (SMA), both virtual and hardware versions

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

Indicators of Compromise

• The indicator of compromise for this vulnerability is an accumulation of TCP connections that will not be freed, which can lead to memory exhaustion. To determine whether there is an accumulation of connections, use the status detail command in the Cisco WSA CLI. The value of the Total client connections field may show a large number of connections, as shown in the following example:
  
  

  # status detail 
  Connections:
    Total client connections                   99999

  
  If this condition is observed, the appliance may have been compromised by this vulnerability. In addition, any indication of memory exhaustion should be examined because this vulnerability is a memory leak.

Workarounds

• If the results of using the status detail command in the Cisco WSA CLI indicate an accumulation of TCP connections, as described in the "Indicators of Compromise" section, use the hidden diagnostic -> PROXY -> KICK command to restart the proxy process and reclaim memory.

Fixed Software

• When considering software upgrades, customers are advised to consult the Cisco Security Advisories 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 upgrade 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.
  
  In the following table, the left column lists major releases of Cisco AsyncOS Software for Cisco WSA. The center column indicates whether a major release is affected by the vulnerability described in this advisory and the first minor release that includes the fix for this vulnerability. The right column indicates whether a major release is affected by all the vulnerabilities described in this and the following companion advisories and which release includes fixes for those vulnerabilities:
  

  • cisco-sa-20151104-aos
  • cisco-sa-20150612-esa
  • cisco-sa-20151104-esa2
  • cisco-sa-20151104-wsa
  • cisco-sa-20151104-wsa1
  • cisco-sa-20151104-wsa2

  Customers should upgrade to an appropriate release as indicated in the following table:
  
  

  AsyncOS for WSA Major Release	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Companion Advisories
  7.5 and prior	Not affected	7.7.0-761 or later
  7.7	Not affected	7.7.0-761 or later
  8.0	8.0.7-151	8.0.8-113 or later
  8.1	Affected; migrate to 8.5.2-004	Affected; migrate to 8.5.3-051 or later
  8.5	8.5.2-004	8.5.3-051 or later
  8.6	Affected; migrate to 8.7.0-171-LD	Affected; migrate to 8.7.0-171-LD or later
  8.7	8.7.0-171-LD	8.7.0-171-LD or later
  8.8	8.8.0-085	8.8.0-085 or later
  9.0	Not affected	Not affected

  
  

  In most cases a WSA can be updated over the network by using the System Upgrade options in the System Administration GUI. To upgrade a device by using the System Administration GUI:

  1. Choose System Administration > System Upgrade.
  2. Click Upgrade Options.
  3. Choose the option to Download and Install or, for an ESA, Download the upgrade.
  4. Choose the release to upgrade to.
  5. In the Upgrade Preparation area, choose the appropriate options.
  6. Click Proceed to begin the upgrade. A progress bar displays the status of the upgrade.

  After the upgrade is complete, the device reboots.

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.

Source

• This vulnerability was found during the resolution of a support case.

URL

• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151104-wsa1

Revision History

• Version	Description	Section	Status	Date
  1.1	Added steps for upgrading a device by using the GUI.	Fixed Software	Final	2015-November-20
  1.0	Initial public release.	—	Final	2015-November-04

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