Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software IKEv2 Certificate Authentication Denial of Service Vulnerability

Description

A vulnerability in the certification authentication feature of Internet Key Exchange version 2 (IKEv2) for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload unexpectedly. This vulnerability is due to a logic error during the certificate authentication phase of the IKEv2 connection setup. An attacker could exploit this vulnerability by attempting to establish an IKEv2 VPN connection with a crafted certificate. A successful exploit could allow the attacker to cause the IKEv2 process to crash, causing a denial of service (DoS) condition. 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-asaftd-ikev2cert-dos-uWyc2xtv 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 . Security Impact Rating: High CVE: CVE-2026-20249

What to do

Install the fixed versions listed in the official advisory. If you cannot update right away, apply the workarounds or mitigations it describes and limit access to the affected service.

Details

Vendor

Cisco

Product

Cisco ASA / FTD

CVE

CVE-2026-20249

Affected versions

Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.16: 37 versions, from 9.16.1 to 9.16.4.92
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.18: 32 versions, from 9.18.1 to 9.18.4.135
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.19: 13 versions, from 9.19.1 to 9.19.1.42
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.20: 22 versions, from 9.20.1 to 9.20.4.30
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.23: 9 versions, from 9.23.1 to 9.23.1.195
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.22: 12 versions, from 9.22.1.1 to 9.22.3
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.24: 4 versions, from 9.24.1 to 9.24.1.155
Cisco Secure Firewall Threat Defense (FTD) Software 7.0: 17 versions, from 7.0.0 to 7.0.9
Cisco Secure Firewall Threat Defense (FTD) Software 7.2: 18 versions, from 7.2.0 to 7.2.11
Cisco Secure Firewall Threat Defense (FTD) Software 7.3: 4 versions, from 7.3.0 to 7.3.1.2
Cisco Secure Firewall Threat Defense (FTD) Software 7.4: 11 versions, from 7.4.0 to 7.4.7
Cisco Secure Firewall Threat Defense (FTD) Software 7.6: 5 versions, from 7.6.0 to 7.6.4
Cisco Secure Firewall Threat Defense (FTD) Software 7.7: 4 versions, from 7.7.0 to 7.7.11
Cisco Secure Firewall Threat Defense (FTD) Software 10.0: 10.0.0 (from the advisory and NVD; check the exact builds in the official advisory)

CVSS score

8.6

Actively exploited

Not known at this time

Source

Cisco PSIRT – original advisory

Published

September 18, 2026

The description and the recommended action are quoted from the public advisory (the action is our generic advice); severity, exploitation status and affected versions are compiled automatically from public sources and may contain errors. The vendor's original advisory prevails: check it before taking action. This information is provided without warranty and does not replace a professional assessment.