CVE-2026-20039 Denial of service in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software

High 8.6 Published 4 Mar 2026 Updated 5 Mar 2026

Unauthenticated remote attackers can cause a denial of service on Cisco ASA and FTD devices by sending crafted HTTP requests to the VPN web server.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-20039?

CVE-2026-20039 is a high-severity denial of service vulnerability in Cisco Adaptive Security Appliance Software, published on 4 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-244

Which versions are affected by CVE-2026-20039?

It affects 2 products.

Products include Cisco Adaptive Security Appliance Software, Cisco Secure Firewall Threat Defense.

How do I fix CVE-2026-20039?

No fix has been published for CVE-2026-20039 yet. Limit exposure of the affected software until one is available.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-20039 being exploited?

There is no known exploitation of CVE-2026-20039 in the wild and no public exploit code.

All Cisco Adaptive Security Appliance Software vulnerabilities

Sources

Also known as GHSA-ch3j-whf9-3xp2.