Summary

• A vulnerability in the implementation of the proprietary SSH stack with SSH key-based authentication in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to log in to a Cisco Secure Firewall ASA device and execute commands as a specific user.

  This vulnerability is due to insufficient validation of user input during the SSH authentication phase. An attacker could exploit this vulnerability by submitting crafted input during SSH authentication to an affected device. A successful exploit could allow the attacker to log in to the device as a specific user without the private SSH key of that user. To exploit this vulnerability, the attacker must possess a valid username and the associated public key. The private key is not required.

  Notes:

  • Exploitation of this vulnerability does not provide the attacker with root access.
  • The authentication, authorization, and accounting (AAA) configuration command auto-enable is not affected by this vulnerability.  

  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-ssh-keybypass-cr5xPUSf

  This advisory is part of the March 2026 release of the Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2026 Semiannual Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco products if they were running a vulnerable release of Cisco Secure Firewall ASA Software and the following conditions were met:

  • The Cisco SSH stack was enabled. The Cisco SSH stack was first introduced in Cisco Secure Firewall ASA Software Release 9.17.1.
  • The device was configured for SSH key-based authentication.
  • SSH access was allowed on at least one interface.

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

  Determine Whether the Cisco SSH Stack Is Enabled

  To determine whether the CiscoSSH stack is enabled on a device, use the show running-config | include ssh command. Verify the presence of the ssh stack ciscossh configuration and an SSH ACL, as shown in the following example:

  ciscoasa# show running-config | include ssh
  aaa authentication ssh console LOCAL
  ssh scopy enable
  ssh stack ciscossh
  ssh stricthostkeycheck
  ssh timeout 5
  ssh version 2
  ssh key-exchange group dh-group14-sha256
  ssh 0.0.0.0 0.0.0.0 management
  ciscoasa#

  In the preceding example, SSH is accessible only through the management interface. If the output does not contain ssh stack ciscossh, the device is not affected by this vulnerability.

  Determine Whether SSH Key-Based Authentication Is Enabled

  To determine whether SSH key-based authentication is enabled on a device, use the show running-config | include ssh command. Verify the presence of the ssh authentication publickey configuration, as shown in the following example:

  ciscoasa# show run | include ssh
  aaa authentication ssh console LOCAL
  ssh scopy enable
  ssh stack ciscossh
  ssh stricthostkeycheck
  ssh timeout 5
  ssh version 2
  ssh key-exchange group dh-group14-sha256
  ssh 0.0.0.0 0.0.0.0 management
  ssh authentication publickey ...
  ciscoasa#

   

  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 Firewall Threat Defense (FTD) Software
  • Secure Firewall Management Center (FMC) Software

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To fully remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.

  Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software

  To help customers determine their exposure to vulnerabilities in Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software, Cisco provides the Cisco Software Checker. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”).

  To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to search for vulnerabilities that affect a specific software release. To use the form, follow these steps:

  1. Choose which advisories the tool will search—all advisories, only advisories with a Critical or High Security Impact Rating (SIR), or only this advisory.
  2. Choose the appropriate software.
  3. Choose the appropriate platform.
  4. Enter a release number—for example, 9.20.3.4 for Cisco Secure Firewall ASA Software or 7.4.2 for Cisco Secure FTD Software.
  5. Click Check.

  Only this advisory All Critical and High advisories All advisories Cisco ASA Software Cisco FMC Software Cisco FTD Software Any Platform 3000 Series Industrial Security Appliances (ISA) ASA 5500-X Series Firewalls ASA Service Module Adaptive Security Virtual Appliance (ASAv) Firepower 1000 Series Firepower 2100 Series Firepower 4100 Series Firepower 9000 Series Secure Firewall 1200 Series Secure Firewall 3100 Series Secure Firewall 4200 Series

   

   

  Additional Resources

  For help determining the best Cisco Secure Firewall ASA, Secure FMC, or Secure FTD Software release, see the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.

  Cisco Secure Firewall ASA Compatibility
  Cisco Secure Firewall ASA Upgrade Guide
  Cisco Secure Firewall Threat Defense Compatibility Guide

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 internal security testing by T.VE of the Cisco Advanced Security Initiatives Group (ASIG).

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ssh-keybypass-cr5xPUSf

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2026-MAR-04

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