Summary

• A vulnerability in the SAML authentication process of Cisco Secure Client could allow an unauthenticated, remote attacker to conduct a carriage return line feed (CRLF) injection attack against a user.

  This vulnerability is due to insufficient validation of user-supplied input. An attacker could exploit this vulnerability by persuading a user to click a crafted link while establishing a VPN session. A successful exploit could allow the attacker to execute arbitrary script code in the browser or access sensitive, browser-based information, including a valid SAML token. The attacker could then use the token to establish a remote access VPN session with the privileges of the affected user. Individual hosts and services behind the VPN headend would still need additional credentials for successful access.

  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-secure-client-crlf-W43V4G7

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco Secure Client and the VPN headend is configured with the SAML External Browser feature:

  • Secure Client for Linux
  • Secure Client for macOS
  • Secure Client for Windows

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

  Determine the VPN Headend Configuration

  To determine whether the VPN headend is configured to use the SAML External Browser feature, use the show running-config tunnel-group privileged EXEC command in the Cisco Adaptive Security Appliance (ASA) Software or Cisco Firepower Threat Defense (FTD) Software CLI.

  The following examples show the output of the command for a device that has the SAML External Browser feature enabled. This output is different based on the software release that is running on the device:

  ciscoasa# show running-config tunnel-group
  tunnel-group EXAMPLE_GROUP type remote-access
  tunnel-group EXAMPLE_GROUP webvpn-attributes
   authentication saml
   saml external-browser
   saml identity-provider EXAMPLE
  
  ciscoasa# show running-config tunnel-group
  tunnel-group EXAMPLE_GROUP type remote-access
  tunnel-group EXAMPLE_GROUP webvpn-attributes
   authentication saml
   external-browser enable
   saml identity-provider https://example.com

  
  

  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:

  • Secure Client AnyConnect for Android
  • Secure Client (including AnyConnect) for Universal Windows Platform
  • Secure Client AnyConnect VPN for iOS

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, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.

  Cisco Secure Client Release	First Fixed Release
  Earlier than 4.10.04065	Not vulnerable.
  4.10.04065 and later	4.10.08025
  5.0	Migrate to a fixed release.
  5.1	5.1.2.42

  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 Paulos Yibelo Mesfin of Amazon Security for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-secure-client-crlf-W43V4G7

Revision History

• Version	Description	Section	Status	Date
  1.1	Added example CLI output for recent software releases.	Vulnerable Products	Final	2024-MAR-12
  1.0	Initial public release.	-	Final	2024-MAR-06

  Show Less