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 ["#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 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 ["https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-notice-jfxK98ZP"]. 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 ["https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hardening-asaftdfmc-uvpPROhN"].

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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 ["#fs"] section of this advisory.

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Products Confirmed Not Vulnerable: Only products listed in the Vulnerable Products ["#vp"] 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.

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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 ["https://bst.cloudapps.cisco.com/bugsearch/bug/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 ["https://bst.cloudapps.cisco.com/bugsearch/bug/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

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Workarounds: There are no workarounds that address these vulnerabilities.

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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 ["https://sec.cloudapps.cisco.com/security/center/softwarechecker.x"]. 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 ["https://sec.cloudapps.cisco.com/security/center/softwarechecker.x"] 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: Choose which advisories the tool will search—all advisories, only advisories with a Critical or High Security Impact Rating (SIR) ["https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#asr"], or only this advisory. Choose the appropriate software. Choose the appropriate platform. 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. 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 Firepower NGFW Virtual Secure Firewall 1200 Series Secure Firewall 3100 Series Secure Firewall 4200 Series Firepower Management Center Appliances For instructions on upgrading a Cisco Secure FTD device, see the appropriate Cisco Secure FMC upgrade guide ["https://www.cisco.com/c/en/us/support/security/defense-center/products-installation-guides-list.html"]. 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 ["https://www.cisco.com/c/en/us/td/docs/security/asa/compatibility/asamatrx.html"] Cisco Secure Firewall ASA Upgrade Guide ["https://www.cisco.com/c/en/us/td/docs/security/asa/upgrade/asa-upgrade/planning.html"] Cisco Secure Firewall Threat Defense Compatibility Guide ["https://www.cisco.com/c/en/us/td/docs/security/secure-firewall/compatibility/threat-defense-compatibility.html"]

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Vulnerability Policy: To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy ["http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html"]. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco. For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model ["https://sec.cloudapps.cisco.com/security/center/resources/risk-based-disclosure"].

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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.

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

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Legal Disclaimer: SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT The Cisco Support and Downloads ["https://www.cisco.com/c/en/us/support/index.html"] 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. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid. 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 Technical Assistance Center (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. When considering software upgrades ["https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes"], customers are advised to regularly consult the advisories ["https://www.cisco.com/go/psirt"] for the relevant Cisco products 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) ["https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html"] or their contracted maintenance providers. LEGAL DISCLAIMER DETAILS CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME. Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories ["https://www.cisco.com/go/psirt"] page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy ["https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html#fixes"] for more information.