---
id: CVE-2019-1691
title: >-
  A vulnerability in the detection engine of Cisco Firepower Threat Defense
  Software could allow an unauthenticated, remote attacker to cause the
  unexpected restart of the SNORT detection engine, resulting in a denial of
  service (DoS) cond…
summary: >-
  A vulnerability in the detection engine of Cisco Firepower Threat Defense
  Software could allow an unauthenticated, remote attacker to cause the
  unexpected restart of the SNORT detection engine, resulting in a denial of
  service (DoS) cond…
severity: medium
cvss: 5.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L'
cwe:
  - CWE-20
  - CWE-755
vendor: cisco
product: secure_firewall_threat_defense
affected:
  - secure_firewall_threat_defense < 6.2.3.4
patched:
  - secure_firewall_threat_defense 6.2.3.4
published: '2019-02-21'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2019-1691'
references:
  - url: 'http://www.securityfocus.com/bid/107099'
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190220-fpwr-ssltls-dos
    label: psirt@cisco.com
  - url: 'http://www.securityfocus.com/bid/107099'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190220-fpwr-ssltls-dos
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.02265
epssPercentile: 0.82261
ingestedAt: '2026-08-11T19:48:26.044Z'
---

## Overview

A vulnerability in the detection engine of Cisco Firepower Threat Defense Software could allow an unauthenticated, remote attacker to cause the unexpected restart of the SNORT detection engine, resulting in a denial of service (DoS) condition. The vulnerability is due to the incomplete error handling of the SSL or TLS packet header during the connection establishment. An attacker could exploit this vulnerability by sending a crafted SSL or TLS packet during the connection handshake. An exploit could allow the attacker to cause the SNORT detection engine to unexpectedly restart, resulting in a partial DoS condition while the detection engine restarts. Versions prior to 6.2.3.4 are affected.

## Affected

- `secure_firewall_threat_defense < 6.2.3.4`

## Remediation

Upgrade past the affected range:

- `secure_firewall_threat_defense 6.2.3.4`