Cisco Web Security Appliance HTTPS Packet Processing Denial of Service Vulnerability

Summary

• A vulnerability in the web proxy framework of the Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker with the ability to negotiate a secure connection from within the trusted network to cause a denial of service (DoS) condition on the affected device.
  
  The vulnerability is due to incorrect processing of HTTPS packets. An attacker could exploit this vulnerability by sending a malformed HTTPS request packet through the affected device. A successful exploit could allow an attacker to create a DoS condition, causing all requests traversing the WSA to be dropped. The condition is temporary and no manual intervention is required to restore functionality.
  
  Cisco has released software updates that address this vulnerability. Workarounds that mitigate this vulnerability are not available.
  
  This advisory is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160302-wsa

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Web Security Appliance (WSA), both virtual and hardware versions, running AsyncOS prior to 8.5.3-051 and 9.0.0-485.
  
  To determine the software version running on the WSA, use the version command. The following example shows the output of this command on a system running software version 7.5.1-079:
  

  ciscowsa> version
  Current Version
  ===============
  Product: Cisco IronPort S670 Web Security Appliance
  Model: S670
  Version: 7.5.1-079
  

  
  The HTTPS Proxy feature must be enabled for a device to be affected by this vulnerability.
  
  To determine if the HTTPS Proxy feature is enabled on the WSA, complete the following steps:
  
  

  1. Login to the WSA's web management interface.
  2. Navigate to Security Services > HTTPS Proxy.
  3. Confirm the status of the feature. The HTTPS Proxy feature is enabled if the Enable HTTPS Proxy setting is checked.

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by this vulnerability.
  
  Cisco has confirmed that this vulnerability does not affect the following Cisco products:

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

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license: http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html
  
  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.
  
  When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses 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.
  
  Customers Without Service Contracts
  
  Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco Technical Assistance Center (TAC): http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html
  
  Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.
  
  This vulnerability has been fixed in Cisco Web Security Appliance (WSA) software versions 8.5.3-051 and later and 9.0.0-485 and later.
  
  In most cases a WSA can be updated over the network by using the System Upgrade option in the System Administration GUI. To upgrade a device by using the System Administration GUI, complete the following steps:
  

  1. Choose System Administration > System Upgrade.
  2. Click Upgrade Options.
  3. Choose Download option.
  4. Choose the desired release for the upgrade.
  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.

URL

• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160302-wsa

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2016-March-02

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