Secure Firewall ASA and FTD
CVE-2026-20039: Cisco Adaptive Security Appliance and Firepower Threat Defense Software SSL VPN Authentication Denial of Service Vulnerability
A vulnerability in the VPN web server 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 a denial of service (DoS) condition on an affected device.
Published
ExploitedNot in CISA KEV
Ransomware useNot reportedPer CISA
SeverityHIGHCVSS 3.1 8.6
EPSS0.36%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 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.17 | 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 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | 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 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | 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 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | 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 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | 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 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.17 | 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 9.12 | 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 9.12 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.17 | 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 9.12 | 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 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | 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 9.12 | 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 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.12 | 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 9.17 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Secure Firewall Adaptive Security Appliance (ASA) Software 9.17 | 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 9.19 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | 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 7.1 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.1 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 6.4 | 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 7.0 | See the advisory |
| Cisco Secure Firewall Threat Defense (FTD) Software 7.1 | 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 6.4 | 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 7.1 | 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 6.4 | 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 6.4 | 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 7.4 | 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 7.4 | See the advisory |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
A vulnerability in the VPN web server 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 a denial of service (DoS) condition on an affected device.
This vulnerability is due to ineffective memory management of the VPN web server. An attacker could exploit this vulnerability by sending a large number of crafted HTTP requests to an affected device. A successful exploit could allow the attacker to cause the device to reload, resulting in a DoS condition.
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.