CVE-2021-1504: Cisco Adaptive Security Appliance Software

High severity, CVSS 7.5. EPSS: 1.7% chance of exploitation in the next 30 days.

Multiple vulnerabilities in Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. These vulnerabilities are due to lack of proper input validation of the HTTPS request. An attacker could exploit these vulnerabilities by sending a crafted HTTPS request to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. Note: This vulnerability affects only specific AnyConnect and WebVPN configurations. For more information, see the Vulnerable Products section.

Affected products

• Cisco Adaptive Security Appliance Software: from 9.7, before 9.8.4.35 (fixed in 9.8.4.35); from 9.9, before 9.9.2.85 (fixed in 9.9.2.85); from 9.10, before 9.12.4.10 (fixed in 9.12.4.10); from 9.13, before 9.13.1.21 (fixed in 9.13.1.21); from 9.14, before 9.14.2.4 (fixed in 9.14.2.4); from 9.15, before 9.15.1.7 (fixed in 9.15.1.7)
• Cisco Secure Firewall Threat Defense: from 6.5.0, before 6.6.4 (fixed in 6.6.4); from 6.7.0, before 6.7.0.1 (fixed in 6.7.0.1)

Published 2021-04-29. Last modified 2026-08-11.