Summary

• Update from October 22nd, 2020: Cisco has become aware of a new Cisco Adaptive Security Appliance vulnerability that could affect the fixed releases recommended for code trains 9.13 and 9.14 in the Fixed Software section of this advisory. See the Cisco Adaptive Security Appliance Software SSL/TLS Denial of Service Vulnerability for additional information.

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  A vulnerability in the SSL VPN negotiation process for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a reload of an affected device, resulting in a denial of service (DoS) condition.

  The vulnerability is due to inefficient direct memory access (DMA) memory management during the negotiation phase of an SSL VPN connection. An attacker could exploit this vulnerability by sending a steady stream of crafted Datagram TLS (DTLS) traffic to an affected device. A successful exploit could allow the attacker to exhaust DMA memory on the device and cause a DoS condition.

  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-asaftd-sslvpndma-dos-HRrqB9Yx

  This advisory is part of the October 2020 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication, which includes 17 Cisco Security Advisories that describe 17 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: October 2020 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco products if they are running a vulnerable release of Cisco ASA Software or FTD Software and have Clientless SSL VPN or AnyConnect SSL VPN configured.

  For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.

  Determine Whether an SSL VPN Is Configured

  To determine whether Clientless SSL VPN or AnyConnect SSL VPN is enabled on a device, use the show running-config webvpn command. The following example shows the output of the command for a device that has Clientless SSL VPN or AnyConnect SSL VPN enabled:

  cisco# show running-config webvpn
  webvpn
  .
  .
  .
   enable <interface_name>
  .
  .
  .

   

  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 Cisco Firepower Management Center (FMC) Software.

Indicators of Compromise

• Exploitation of this vulnerability could cause an affected device to run low on DMA memory. To check whether Free memory is decreasing without increasing, use the show memory detail | begin MEMPOOL_DMA command and monitor the output, which is shown in the following example:

  device(config)# show memory detail | begin MEMPOOL_DMA
  MEMPOOL_DMA POOL STATS: 
  
  Non-mmapped bytes allocated = 222298112 
  Number of free chunks = 162 
  Number of mmapped regions = 0 
  Mmapped bytes allocated = 0 
  Max memory footprint = 222298112 
  Keepcost = 3264 
  Max contiguous free mem = 3264 
  Allocated memory in use = 222259824 
  Free memory = 38288

  If the value of the Free memory counter decreases quickly for a sustained period of time, administrators are advised to contact the Cisco Technical Assistance Center (TAC) for further investigation.

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 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(s), the left column lists Cisco software releases. The center column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by any of the vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.

  Cisco ASA Software

  Cisco ASA Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
  Earlier than 9.61	Migrate to a fixed release.	Migrate to a fixed release.
  9.61	9.6.4.45	9.6.4.45
  9.71	Migrate to a fixed release.	Migrate to a fixed release.
  9.8	9.8.4.29	9.8.4.29
  9.9	9.9.2.80	9.9.2.80
  9.10	9.10.1.44	9.10.1.44
  9.12	9.12.4.4	9.12.4.4
  9.13	9.13.1.13	9.13.1.13
  9.14	9.14.1.30	9.14.1.30

  1. Cisco ASA Software releases 9.7 and earlier have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  Cisco FTD Software

  Cisco FTD Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
  Earlier than 6.2.21	Migrate to a fixed release.	Migrate to a fixed release.
  6.2.2	Migrate to a fixed release.	Migrate to a fixed release.
  6.2.3	Migrate to a fixed release.	Migrate to a fixed release.
  6.3.0	6.3.0.6 (future release)	Migrate to a fixed release.
  6.4.0	6.4.0.10	Migrate to a fixed release.
  6.5.0	6.5.0.5 (future release)	Migrate to a fixed release.
  6.6.0	6.6.1	6.6.1

  1. Cisco FMC and FTD Software releases 6.0.1 and earlier, as well as releases 6.2.0 and 6.2.1, have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  To upgrade to a fixed release of Cisco FTD Software, do one of the following:

  • For devices that are managed by using Cisco Firepower Management Center (FMC), use the FMC interface to install the upgrade. After installation is complete, reapply the access control policy.
  • For devices that are managed by using Cisco Firepower Device Manager (FDM), use the FDM interface to install the upgrade. After installation is complete, reapply the access control policy.

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-asaftd-sslvpndma-dos-HRrqB9Yx

Revision History

• Version	Description	Section	Status	Date
  2.0	Updated the Summary section to provide information on a new vulnerability affecting fixed release recommendations for code trains 9.13 and 9.14.	Summary	Final	2020-OCT-22
  1.0	Initial public release.	—	Final	2020-OCT-21

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