Summary

• A vulnerability in the handler for HTTP authentication for resources accessed through the Clientless SSL VPN portal of Cisco Adaptive Security Appliance (ASA) Software could allow an authenticated, remote attacker to cause a denial of service (DoS) condition on an affected device or to obtain portions of process memory from an affected device.

  This vulnerability is due to insufficient bounds checking when parsing specific HTTP authentication messages. An attacker could exploit this vulnerability by sending malicious traffic to an affected device acting as a VPN Gateway. To send this malicious traffic, an attacker would need to control a web server that can be accessed through the Clientless SSL VPN portal. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition, or to retrieve bytes from the device process memory that may contain sensitive information.
  

  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-asa-ssl-vpn-heap-zLX3FdX

  This advisory is part of the April 2022 release of the Cisco ASA, FTD, and FMC Security Advisory Bundled publication. For a complete list of the advisories and links to them, see Cisco Event Response: April 2022 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 and have Clientless SSL VPN configured.

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

  Determine Whether Clientless SSL VPN is Configured

  To determine whether Clientless SSL VPN is enabled on a device, do both of the following:

  • Use the show running-config webvpn command and verify the presence of the enable command for at least one interface. The following example shows the output of the command for a device that has SSL VPN enabled on the outside interface:
    

    cisco# show running-config webvpn
    webvpn
    .
    .
    .
     enable outside
    .
    .
    .

  • Use the show running-config all group-policy command and verify the presence of the ssl-clientless value in the vpn-tunnel-protocol parameter. The following example shows the output of the command for a device that has Clientless SSL VPN enabled:

    cisco# show running-config all group-policy | include ssl-clientless
    vpn-tunnel-protocol ssl-client ssl-clientless

  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 Cisco products:

  • Firepower Management Center (FMC) Software
  • Firepower Threat Defense (FTD) Software

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 with service contracts that entitle them to regular software updates should obtain security fixes through their usual update channels.

  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.

  The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool.

  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 Critical or High SIR 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
  9.7 and earlier1	Migrate to a fixed release.	Migrate to a fixed release.
  9.8	9.8.4.44 (June 2022)	9.8.4.44 (June 2022)
  9.91	Migrate to a fixed release.	Migrate to a fixed release.
  9.101	Migrate to a fixed release.	Migrate to a fixed release.
  9.12	9.12.4.38	9.12.4.38
  9.131	Migrate to a fixed release.	Migrate to a fixed release.
  9.14	9.14.4	9.14.4
  9.15	9.15.1.21	9.15.1.21
  9.16	9.16.2.14	9.16.2.14
  9.17	9.17.1.7	9.17.1.7

  1. Cisco ASA Software releases 9.7 and earlier as well as releases 9.9, 9.10, and 9.13 have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

Exploitation and Public Announcements

• The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

Source

• Cisco would like to thank Nikita Abramov of Positive Technologies for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ssl-vpn-heap-zLX3FdX

Revision History

• Version	Description	Section	Status	Date
  1.1	Updated ASA 9.8 first fixed release information.	Fixed Software	Final	2022-JUN-01
  1.0	Initial public release.	—	Final	2022-APR-27

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