Summary

• Multiple vulnerabilities in Cisco Secure Firewall Management Center (FMC) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated attacker to perform an sftunnel authentication bypass or sftunnel denial of service (DoS) attack.

  For more information about these vulnerabilities, see the Details section of this advisory.

  Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmcftd-sftun-multivulns-WGVHOrN3

  This advisory is part of a group of advisories. For a complete list of the advisories and links to them, see Cisco Advance Notification for Publication of September 16, 2026, Security Advisories. In addition, for further documentation of improvements and fixes in Cisco Secure Firewall products, see Cisco Secure Firewall Adaptive Security Appliance Software, Secure Firewall Threat Defense Software, and Secure Firewall Management Center Software Hardening Release: September 2026.

Affected Products

• Vulnerable Products

  These vulnerabilities affect Cisco Secure FMC Software and Secure FTD Software, regardless of device configuration.

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

  Products Confirmed Not Vulnerable

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

  Cisco has confirmed that these vulnerabilities do not affect Cisco Secure Firewall Adaptive Security Appliance (ASA) Software.

Details

• The vulnerabilities are not dependent on one another. Exploitation of one of the vulnerabilities is not required to exploit the other vulnerability. In addition, a software release that is affected by one of the vulnerabilities may not be affected by the other vulnerability.

  Details about the vulnerabilities are as follows:

  CVE-2026-20295: Cisco Secure FMC Software and Secure FTD Software sftunnel Memory Exhaustion DoS Vulnerability

  A vulnerability in the sftunnel inter-device communication protocol of Cisco Secure FMC Software and Cisco Secure FTD Software could allow an unauthenticated, remote attacker to exhaust the available memory of an affected device.

  This vulnerability is due to improper management of memory resources during sftunnel TLS connection setup. An attacker could exploit this vulnerability by sending crafted sftunnel TLS frames to an affected device during the connection setup. A successful exploit could allow the attacker to exhaust the available memory on the affected device, which could result in a DoS condition.

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

  Bug ID(s): CSCws43281
  CVE ID: CVE-2026-20295
  Security Impact Rating (SIR): High
  CVSS Base Score: 8.6
  CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

  CVE-2026-20323: Cisco Secure FMC Software and Secure FTD Software sftunnel Unauthorized Authentication Bypass Vulnerability

  A vulnerability in the sftunnel inter-device communication protocol of Cisco Secure FMC Software and Cisco Secure FTD Software could allow an unauthenticated, adjacent attacker to impersonate the peer device and obtain access at the level of the manager role, which is equivalent to root.

  This vulnerability is due to improper management of the TLS certificate for the sftunnel management connection. An attacker could exploit this vulnerability by connecting to the sftunnel port using a crafted TLS certificate. A successful exploit could allow the attacker to become a registered sftunnel peer with root access.

  Note: The attack is successful only if the sftunnel connection is down or the attack can disrupt the sftunnel connection long enough to execute the attack.

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

  Bug ID(s): CSCwu16917
  CVE ID: CVE-2026-20323
  Security Impact Rating (SIR): High
  CVSS Base Score: 8.3
  CVSS Vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

Workarounds

• There are no workarounds that address these vulnerabilities.

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 remediate these vulnerabilities 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

   

  For instructions on upgrading a Cisco Secure FTD device, see the appropriate Cisco Secure FMC upgrade guide.

  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 vulnerabilities that are described in this advisory.

Source

• Cisco would like to thank Mark Pralat, an independent security researcher, for reporting these vulnerabilities.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-fmcftd-sftun-multivulns-WGVHOrN3

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2026-SEP-16

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