---
id: CVE-2021-1402
title: >-
  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 (D…
summary: >-
  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 (D…
severity: high
cvss: 8.6
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H'
cwe:
  - CWE-119
  - CWE-20
vendor: cisco
product: secure_firewall_threat_defense
affected:
  - 'secure_firewall_threat_defense >= 6.3.0, < 6.4.0'
  - 'secure_firewall_threat_defense >= 6.5.0, < 6.6.0'
patched:
  - secure_firewall_threat_defense 6.6.0
published: '2021-04-29'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-1402'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-ssl-decrypt-dos-DdyLuK6c
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-ssl-decrypt-dos-DdyLuK6c
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01386
epssPercentile: 0.71053
ingestedAt: '2026-08-18T12:28:06.951Z'
---

## Overview

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

- `secure_firewall_threat_defense >= 6.3.0, < 6.4.0`
- `secure_firewall_threat_defense >= 6.5.0, < 6.6.0`

## Remediation

Upgrade past the affected range:

- `secure_firewall_threat_defense 6.6.0`