---
id: CVE-2020-3191
title: >-
  A vulnerability in DNS over IPv6 packet processing for Cisco Adaptive Security
  Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could
  allow an unauthenticated, remote attacker to cause the device to unexpectedly
  reloa…
summary: >-
  A vulnerability in DNS over IPv6 packet processing for Cisco Adaptive Security
  Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could
  allow an unauthenticated, remote attacker to cause the device to unexpectedly
  reloa…
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-20
  - CWE-20
vendor: cisco
product: secure_firewall_threat_defense
affected:
  - 'secure_firewall_threat_defense >= 6.2.3, < 6.2.3.16'
  - 'secure_firewall_threat_defense >= 6.3.0, < 6.3.0.6'
  - 'secure_firewall_threat_defense >= 6.4.0, < 6.4.0.6'
  - asa_5505_firmware = 9.4(1)
  - asa_5505_firmware = 96.4(0.42)
  - asa_5510_firmware = 9.4(1)
  - asa_5510_firmware = 96.4(0.42)
  - asa_5512-x_firmware = 9.4(1)
  - asa_5512-x_firmware = 96.4(0.42)
  - asa_5515-x_firmware = 9.4(1)
  - asa_5515-x_firmware = 96.4(0.42)
  - asa_5520_firmware = 9.4(1)
  - asa_5520_firmware = 96.4(0.42)
  - asa_5525-x_firmware = 9.4(1)
  - asa_5525-x_firmware = 96.4(0.42)
  - asa_5540_firmware = 9.4(1)
  - asa_5540_firmware = 96.4(0.42)
  - asa_5545-x_firmware = 9.4(1)
  - asa_5545-x_firmware = 96.4(0.42)
  - asa_5550_firmware = 9.4(1)
  - asa_5550_firmware = 96.4(0.42)
  - asa_5555-x_firmware = 9.4(1)
  - asa_5555-x_firmware = 96.4(0.42)
  - asa_5580_firmware = 9.4(1)
  - asa_5580_firmware = 96.4(0.42)
  - asa_5585-x_firmware = 9.4(1)
  - asa_5585-x_firmware = 96.4(0.42)
  - 'adaptive_security_appliance_software >= 9.6, < 9.6.4.36'
  - 'adaptive_security_appliance_software >= 9.8, < 9.8.4.12'
  - 'adaptive_security_appliance_software >= 9.9, < 9.9.2.66'
  - 'adaptive_security_appliance_software >= 9.10, < 9.10.1.37'
  - 'adaptive_security_appliance_software >= 9.12, < 9.12.2.9'
patched:
  - secure_firewall_threat_defense 6.4.0.6
  - adaptive_security_appliance_software 9.12.2.9
published: '2020-05-06'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-3191'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ipv6-67pA658k
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ipv6-67pA658k
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01864
epssPercentile: 0.78383
ingestedAt: '2026-08-11T19:48:27.548Z'
---

## Overview

A vulnerability in DNS over IPv6 packet processing for Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to unexpectedly reload, resulting in a denial of service (DoS) condition. The vulnerability is due to improper length validation of a field in an IPv6 DNS packet. An attacker could exploit this vulnerability by sending a crafted DNS query over IPv6, which traverses the affected device. An exploit could allow the attacker to cause the device to reload, resulting in a DoS condition. This vulnerability is specific to DNS over IPv6 traffic only.

## Affected

- `secure_firewall_threat_defense >= 6.2.3, < 6.2.3.16`
- `secure_firewall_threat_defense >= 6.3.0, < 6.3.0.6`
- `secure_firewall_threat_defense >= 6.4.0, < 6.4.0.6`
- `asa_5505_firmware = 9.4(1)`
- `asa_5505_firmware = 96.4(0.42)`
- `asa_5510_firmware = 9.4(1)`
- `asa_5510_firmware = 96.4(0.42)`
- `asa_5512-x_firmware = 9.4(1)`
- `asa_5512-x_firmware = 96.4(0.42)`
- `asa_5515-x_firmware = 9.4(1)`
- `asa_5515-x_firmware = 96.4(0.42)`
- `asa_5520_firmware = 9.4(1)`
- `asa_5520_firmware = 96.4(0.42)`
- `asa_5525-x_firmware = 9.4(1)`
- `asa_5525-x_firmware = 96.4(0.42)`
- `asa_5540_firmware = 9.4(1)`
- `asa_5540_firmware = 96.4(0.42)`
- `asa_5545-x_firmware = 9.4(1)`
- `asa_5545-x_firmware = 96.4(0.42)`
- `asa_5550_firmware = 9.4(1)`
- `asa_5550_firmware = 96.4(0.42)`
- `asa_5555-x_firmware = 9.4(1)`
- `asa_5555-x_firmware = 96.4(0.42)`
- `asa_5580_firmware = 9.4(1)`
- `asa_5580_firmware = 96.4(0.42)`
- `asa_5585-x_firmware = 9.4(1)`
- `asa_5585-x_firmware = 96.4(0.42)`
- `adaptive_security_appliance_software >= 9.6, < 9.6.4.36`
- `adaptive_security_appliance_software >= 9.8, < 9.8.4.12`
- `adaptive_security_appliance_software >= 9.9, < 9.9.2.66`
- `adaptive_security_appliance_software >= 9.10, < 9.10.1.37`
- `adaptive_security_appliance_software >= 9.12, < 9.12.2.9`

## Remediation

Upgrade past the affected range:

- `secure_firewall_threat_defense 6.4.0.6`
- `adaptive_security_appliance_software 9.12.2.9`