Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software for Secure Firewall 3100 and 4200 Series DTLS Denial of Service Vulnerability

Description

A vulnerability in Datagram TLS (DTLS) message handling of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software for Cisco Secure Firewall 3100 Series and 4200 Series devices could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to improper resource management when processing certain DTLS messages. An attacker could exploit this vulnerability by sending a crafted stream of DTLS traffic to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition. Cisco has released software updates that address this vulnerability. There are 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-dtls-dos-Kp57HkyO 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-2026-20250

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-2026-20250

Affected versions

Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.23: 7 versions, from 9.23.1 to 9.23.1.26
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.22: 9 versions, from 9.22.1.1 to 9.22.2.20
Cisco Secure Firewall Adaptive Security Appliance (ASA) Soft 9.24: 9.24.1
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.