Secure Firewall ASA and FTD
CVE-2026-20248: Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense Software TCP DNS Denial of Service Vulnerability
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.
Published
ExploitedNot in CISA KEV
Ransomware useNot reportedPer CISA
SeverityMEDIUMCVSS 3.1 6.8
EPSS0.34%Chance of exploitation in 30 days
Public exploitNot tracked
FixNot yet
Automatic summary from the vendor's CVE record. We haven't written a full analysis of this vulnerability yet.
Affected and fixed versions
| Product / branch | Fixed in |
|---|---|
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.24 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.24 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.24 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.22 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.24 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.23 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.24 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.20 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.3 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.3 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.3 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.3 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.6 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.7 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.6 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.6 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.7 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.7 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.6 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.7 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.6 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 10.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.2 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.4 | See the advisory |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
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.
Exploitation
The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
Sources
KEV status, EPSS score and vendor data refreshed automatically, last on 11 Oct 2026.