Summary

• A vulnerability in the email message filtering feature of Cisco AsyncOS for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to cause an ESA device to become unavailable due to a denial of service (DoS) condition.
  
  The vulnerability is due to improper input validation when an email attachment contains corrupted fields and is filtered by the ESA. An attacker could exploit this vulnerability by sending a crafted email with an attachment to the ESA. A successful exploit could allow the attacker to cause a DoS condition. While the attachment is being filtered, memory is consumed at at high rate until the filtering process restarts. When the process restarts, it will resume processing the same malformed attachment and the DoS condition will continue.
  Cisco has released software updates that address this vulnerability. There are no workarounds that mitigate this vulnerability.
  
  This advisory is available at the following link:
  http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151104-esa2

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco AsyncOS for ESA on both virtual and and hardware appliances.
  
  A message filter that is configured with any of the following rules could allow for the vulnerability to occur:
  

  • body-contains
  • attachment-contains
  • every-attachment-contains
  • attachment-binary-contains
  • dictionary-match
  • attachment-dictionary-match

  To determine which ESA message filters are configured on a device, use the filters detail all command in the ESA CLI. the following example shows the results for a device that is configured to use a generic message filter:
  

  esa.prompt> filters detail all
  
  Num Active Valid Names
        1   Y          Y    example_filter
  example_filter: if body-contains("example", 1) {
                                quarantine("Policy");
                            }

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

  ciscoesa> version
  Current Version
  ===============
  Product: Cisco IronPort X1070 Messaging Gateway(tm) Appliance
  Model: X1070
  Version: 8.5.3-051
  .
  .
  .

  
  
  Cisco Cloud Email Security (CES) includes the Cisco ESA and Cisco Security Management Appliance (SMA) as part of the service solution. Cisco provides regular maintenance of the products included in this solution. Customers can also request a software upgrade by contacting Cisco CES support.

  Products Confirmed Not Vulnerable

  The following products are not affected by this vulnerability:
  

  • Cisco Web Security Appliance, both virtual and hardware versions
  • Cisco Security Mail Appliance, 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 whether traffic is impacted on the ESA. To determine whether traffic is impacted, use the workqueue status command in the ESA CLI. The following example shows the results for an ESA where traffic is impacted:
  

  esa> workqueue status
  Failed to get work queue status: the queue is not mounted
  

  
  If the queue is not mounted, the device may have been compromised by this vulnerability. If the ESA is affected by this vulnerability please contact the Cisco Technical Assistance Center (TAC).

Workarounds

• There are no workarounds that mitigate this vulnerability.

Fixed Software

• When considering software upgrades, customers are advised to consult the Cisco Security Advisories 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.
  
  In the following table, the left column lists major releases of Cisco AsyncOS for ESA software. 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 the following advisories and which release includes fixes for those vulnerabilities:
  

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

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

  AsyncOS for ESA Major Release	First Fixed Release for This Vulnerability	First Fixed Release for This Vulnerability and All Vulnerabilities Described in the Companion Advisories
  7.7 and prior	Affected; migrate to 8.5.7-043	Affected; migrate to 8.5.7-043 or later
  8.0 or 8.0.1	Affected; migrate to 8.5.7-043	Affected; migrate to 8.5.7-043 or later
  8.0.2	Affected; migrate to 9.1.1-023	Affected; migrate to 9.1.1-023 or later
  8.5	8.5.7-043	8.5.7-043 or later
  9.0	Affected; migrate to 9.1.1-023	Affected; migrate to 9.1.1-023 or later
  9.1	9.1.1-023	9.1.1-023 or later
  9.5	Affected; migrate to 9.6.0-046	Affected; migrate to 9.6.0-046 or later
  9.6	9.6.0-046	9.6.0-046 or later
  9.7	Not affected	Not affected

  
  

  In most cases an ESA 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-esa2

Revision History

• Version	Description	Section	Status	Date
  1.2	Added steps for upgrading a device by using the GUI.	Fixed Software	Final	2015-November-20
  1.1	Added information about CES maintenance and upgrades.	Vulnerable Products	Final	2015-November-16
  1.0	Initial public release.	—	Final	2015-November-04

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