CVE-2021-1402: Cisco Secure Firewall Threat Defense

High severity, CVSS 8.6. EPSS: 1.4% chance of exploitation in the next 30 days.

A vulnerability in the software-based SSL/TLS message handler of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message through an affected device. SSL/TLS messages sent to an affected device do not trigger this vulnerability. A successful exploit could allow the attacker to cause a process to crash. This crash would then trigger a reload of the device. No manual intervention is needed to recover the device after the reload.

Affected products

• Cisco Secure Firewall Threat Defense: from 6.3.0, before 6.4.0 (fixed in 6.4.0); from 6.5.0, before 6.6.0 (fixed in 6.6.0)

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