CVE-2026-20248: Cisco Secure Firewall Adaptive Security Appliance ASA Software

Medium severity, CVSS 6.8. EPSS: 0.3% chance of exploitation in the next 30 days.

A vulnerability in the DNS over TCP implementation of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the TCP DNS response handler to unexpectedly restart, causing the device to reload. This vulnerability is due to a logic error when parsing a DNS query and tracking the size of the incoming buffers. An attacker could exploit this vulnerability by formatting a crafted reply to a DNS query sent from the targeted device. A successful exploit could allow the attacker to cause the device to reload, causing a denial of service (DoS) condition. Note: The attacker must be able to respond to DNS queries from the device, either by controlling the DNS service or through a machine-in-the-middle attack.

Affected products

• Cisco Cisco Secure Firewall Adaptive Security Appliance ASA Software: version 9.16.1 only; version 9.16.1.28 only; version 9.16.2 only; version 9.16.2.3 only; version 9.16.2.7 only; version 9.16.2.11 only; …
• Cisco Cisco Secure Firewall Threat Defense FTD Software: version 7.0.0 only; version 7.0.0.1 only; version 7.0.1 only; version 7.0.1.1 only; version 7.0.2 only; version 7.2.0 only; …

Published 2026-09-16. Last modified 2026-09-18.