What’s Vulnerable › Vulnerabilities
CVE-2026-20039: Cisco Adaptive Security Appliance and Firepower Threat Defense Software SSL VPN Authentication Denial of Service Vulnerability
- Severity: high (CVSS 8.6 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-03-04 · updated 2026-08-11
- Weakness: CWE-244
Description
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.
Affected products
- Cisco ASA Software: from 9.12.1 before 9.16.4.84; from 9.17.1 before 9.18.4.57; from 9.19.1 before 9.20.3.16; from 9.22.1.1 before 9.22.2.4; from 9.23.1 before 9.23.1.3 — fixed in 9.16.4.84, 9.18.4.57, 9.20.3.16, 9.22.2.4, 9.23.1.3
- Cisco Firepower Threat Defense Software: from 6.4.0 before 7.0.9; from 7.1.0 before 7.2.10; from 7.3.0 before 7.4.3; from 7.6.0 before 7.6.1; from 7.7.0 before 7.7.10 — fixed in 7.0.9, 7.2.10, 7.4.3, 7.6.1, 7.7.10
How to fix
Upgrade to a fixed version: Cisco ASA Software 9.16.4.84, 9.18.4.57, 9.20.3.16, 9.22.2.4; Cisco Firepower Threat Defense Software 7.0.9, 7.2.10, 7.4.3, 7.6.1. Check the vendor advisory for mitigations.
References
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