Secure Firewall ASA and FTD
CVE-2023-20042: A vulnerability in the AnyConnect SSL VPN feature of Cisco Adaptive Security Appliance (ASA) Software and C…
A vulnerability in the AnyConnect SSL VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.
Published
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 Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.16 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.17 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.18 | See the advisory |
| Cisco Adaptive Security Appliance (ASA) Software 9.19 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.0 | See the advisory |
| Cisco Firepower Threat Defense Software 7.1 | See the advisory |
| Cisco Firepower Threat Defense Software 7.1 | See the advisory |
| Cisco Firepower Threat Defense Software 7.1 | See the advisory |
| Cisco Firepower Threat Defense Software 7.1 | See the advisory |
| Cisco Firepower Threat Defense Software 7.2 | See the advisory |
| Cisco Firepower Threat Defense Software 7.2 | See the advisory |
| Cisco Firepower Threat Defense Software 7.2 | See the advisory |
| Cisco Firepower Threat Defense Software 7.2 | See the advisory |
| Cisco Firepower Threat Defense Software 7.2 | See the advisory |
| Cisco Firepower Threat Defense Software 7.3 | See the advisory |
| Cisco Firepower Threat Defense Software 7.3 | See the advisory |
| Cisco Firepower Threat Defense Software 7.3 | See the advisory |
Always confirm against the vendor advisory, which lists every fixed hotfix.
What it is
A vulnerability in the AnyConnect SSL VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower 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 an implementation error within the SSL/TLS session handling process that can prevent the release of a session handler under specific conditions. An attacker could exploit this vulnerability by sending crafted SSL/TLS traffic to an affected device, increasing the probability of session handler leaks. A successful exploit could allow the attacker to eventually deplete the available session handler pool, preventing new sessions from being established and causing a DoS condition.
Exploitation
The Cisco 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.