Summary

• A vulnerability in the Secure/Multipurpose Internet Mail Extensions (S/MIME) Decryption and Verification or S/MIME Public Key Harvesting features of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to cause an affected device to corrupt system memory. A successful exploit could cause the filtering process to unexpectedly reload, resulting in a denial of service (DoS) condition on the device.

  The vulnerability is due to improper input validation of S/MIME-signed emails. An attacker could exploit this vulnerability by sending a malicious S/MIME-signed email through a targeted device. If Decryption and Verification or Public Key Harvesting is configured, the filtering process could crash due to memory corruption and restart, resulting in a DoS condition. The software could then resume processing the same S/MIME-signed email, causing the filtering process to crash and restart again. A successful exploit could allow the attacker to cause a permanent DoS condition. This vulnerability may require manual intervention to recover the ESA.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190109-esa-dos

Affected Products

• Vulnerable Products

  This vulnerability affects all software versions prior to the first fixed release of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA), both virtual and hardware appliances, if the software is configured for S/MIME Decryption and Verification or S/MIME Public Key Harvesting.
   
  To determine if S/MIME Decryption and Verification is configured on an ESA, an administrator can do the following:

  1. Navigate to Click Mail Policies > Mail Flow Policies.
  2. Navigate through all existing Mail Flow Policies.
  3. Scroll down to the Security Features section on each Mail Flow Policy.
  4. Under S/MIME Decryption/Verification, verify if S/MIME decryption and verification is enabled.

  To determine if S/MIME Public Key Harvesting is configured on an ESA, an administrator can do the following:

  1. Navigate to Click Mail Policies > Mail Flow Policies.
  2. Navigate through all existing Mail Flow Policies.
  3. Scroll down to the Security Features section on each Mail Flow Policy.
  4. Under S/MIME Public Key Harvesting, verify if S/MIME Public Key Harvesting is enabled.

  For additional information on ESA S/MIME capabilities and configuration, please refer to S/MIME Security Services in Email Security Appliance.

  To determine whether a vulnerable release of Cisco AsyncOS Software is running on an ESA, administrators can use the version command in the ESA CLI. The following example shows the output of the command for an ESA that is running Cisco AsyncOS Software Release 10.0.1-087:
  

  ciscoesa> version
  
  Current Version
  ===============
  Product: Cisco C100V Email Security Virtual Appliance
  Model: C100V
  Version: 10.0.1-087
  .
  .
  .

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect the following products:

  • Content Security Management Appliance, virtual and hardware versions
  • Web Security Appliance, virtual and hardware versions

Indicators of Compromise

• Exploitation of this vulnerability could cause the ESA to resume processing the same faulty email message each time the ESA reloads, resulting in a permanent DoS condition. Customers should contact the Cisco Technical Assistance Center (TAC) for recovery procedures.

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:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.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 regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, 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.

  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 TAC:
  https://www.cisco.com/c/en/us/support/web/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.

  Fixed Releases

  In the following table, the left column lists major releases of Cisco AsyncOS Software for ESA. The right 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.
   
  Customers should upgrade to an appropriate release as indicated in the following table:

  Cisco AsyncOS Software for ESA Major Release	First Fixed Release
  Prior to 9.0	Affected; migrate to 11.0.2-044
  9.0.x	Affected; migrate to 11.0.2-044
  10.0.x	Affected; migrate to 11.0.2-044
  11.0.x	11.0.2-0441
  11.1.x	11.1.1-037 or 11.1.2-0232
  12.x	Not vulnerable

  ¹11.0.2-044 will run on all legacy hardware for ESA models x70, x80, and x90 and the virtual appliances.
  ²11.1.1-037 and 12.0.0-281 will run on ESA models x80 and x90 and the virtual appliances.
  
  Note that Cisco provides regular maintenance of products in the Cisco Cloud Email Security (CES) service solution, which includes Cisco Email Security Appliance (ESA) and Cisco Content Security Management Appliance (SMA). Customers can also request a software upgrade by contacting the Cisco TAC.

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 Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190109-esa-dos

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2019-January-09

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