---
id: CVE-2020-3563
title: >-
  A vulnerability in the packet processing functionality of Cisco Firepower
  Threat Defense (FTD) Software could allow an unauthenticated, remote attacker
  to cause a denial of service (DoS) condition on an affected device
summary: >-
  A vulnerability in the packet processing functionality of Cisco Firepower
  Threat Defense (FTD) Software could allow an unauthenticated, remote attacker
  to cause a denial of service (DoS) condition on an affected device. The
  vulnerability…
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-400
  - CWE-400
vendor: cisco
product: secure_firewall_threat_defense
affected:
  - 'secure_firewall_threat_defense >= 6.3.0, < 6.3.0.6'
  - 'secure_firewall_threat_defense >= 6.4.0, < 6.4.0.10'
  - 'secure_firewall_threat_defense >= 6.5.0, < 6.5.0.5'
patched:
  - secure_firewall_threat_defense 6.5.0.5
published: '2020-10-21'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-3563'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-tcp-dos-GDcZDqAf
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-tcp-dos-GDcZDqAf
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01415
epssPercentile: 0.71604
ingestedAt: '2026-08-11T19:48:28.908Z'
---

## Overview

A vulnerability in the packet processing functionality of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to inefficient memory management. An attacker could exploit this vulnerability by sending a large number of TCP packets to a specific port on an affected device. A successful exploit could allow the attacker to exhaust system memory, which could cause the device to reload unexpectedly. No manual intervention is needed to recover the device after it has reloaded.

## Affected

- `secure_firewall_threat_defense >= 6.3.0, < 6.3.0.6`
- `secure_firewall_threat_defense >= 6.4.0, < 6.4.0.10`
- `secure_firewall_threat_defense >= 6.5.0, < 6.5.0.5`

## Remediation

Upgrade past the affected range:

- `secure_firewall_threat_defense 6.5.0.5`