---
id: CVE-2020-3255
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: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-400
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, < 6.4.0.9'
  - asa_5505_firmware = 9.10(1.3)
  - asa_5510_firmware = 9.10(1.3)
  - asa_5512-x_firmware = 9.10(1.3)
  - asa_5515-x_firmware = 9.10(1.3)
  - asa_5520_firmware = 9.10(1.3)
  - asa_5525-x_firmware = 9.10(1.3)
  - asa_5540_firmware = 9.10(1.3)
  - asa_5545-x_firmware = 9.10(1.3)
  - asa_5550_firmware = 9.10(1.3)
  - asa_5555-x_firmware = 9.10(1.3)
  - asa_5580_firmware = 9.10(1.3)
  - asa_5585-x_firmware = 9.10(1.3)
patched:
  - secure_firewall_threat_defense 6.4.0.9
published: '2020-05-06'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-3255'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-dos-N2vQZASR
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-dos-N2vQZASR
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.0184
epssPercentile: 0.78044
ingestedAt: '2026-08-11T19:48:27.714Z'
---

## 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 high rate of IPv4 or IPv6 traffic through an affected device. This traffic would need to match a configured block action in an access control policy. An exploit could allow the attacker to cause a memory exhaustion condition on the affected device, which would result in a DoS for traffic transiting the device, as well as sluggish performance of the management interface. Once the flood is stopped, performance should return to previous states.

## 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, < 6.4.0.9`
- `asa_5505_firmware = 9.10(1.3)`
- `asa_5510_firmware = 9.10(1.3)`
- `asa_5512-x_firmware = 9.10(1.3)`
- `asa_5515-x_firmware = 9.10(1.3)`
- `asa_5520_firmware = 9.10(1.3)`
- `asa_5525-x_firmware = 9.10(1.3)`
- `asa_5540_firmware = 9.10(1.3)`
- `asa_5545-x_firmware = 9.10(1.3)`
- `asa_5550_firmware = 9.10(1.3)`
- `asa_5555-x_firmware = 9.10(1.3)`
- `asa_5580_firmware = 9.10(1.3)`
- `asa_5585-x_firmware = 9.10(1.3)`

## Remediation

Upgrade past the affected range:

- `secure_firewall_threat_defense 6.4.0.9`