---
id: CVE-2020-3577
title: >-
  A vulnerability in the ingress packet processing path of Cisco Firepower
  Threat Defense (FTD) Software for interfaces that are configured either as
  Inline Pair or in Passive mode could allow an unauthenticated, adjacent
  attacker to cause…
summary: >-
  A vulnerability in the ingress packet processing path of Cisco Firepower
  Threat Defense (FTD) Software for interfaces that are configured either as
  Inline Pair or in Passive mode could allow an unauthenticated, adjacent
  attacker to cause…
severity: high
cvss: 7.4
cvssVector: 'CVSS:3.1/AV:A/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 < 6.3.0.6
  - 'secure_firewall_threat_defense >= 6.4.0, < 6.4.0.10'
  - 'secure_firewall_threat_defense >= 6.5.0, < 6.5.0.5'
  - 'secure_firewall_threat_defense >= 6.6.0, < 6.6.1'
patched:
  - secure_firewall_threat_defense 6.6.1
published: '2020-10-21'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-3577'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-inline-dos-nXqUyEqM
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-inline-dos-nXqUyEqM
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00433
epssPercentile: 0.37028
ingestedAt: '2026-08-18T12:28:06.465Z'
---

## Overview

A vulnerability in the ingress packet processing path of Cisco Firepower Threat Defense (FTD) Software for interfaces that are configured either as Inline Pair or in Passive mode could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition. The vulnerability is due to insufficient validation when Ethernet frames are processed. An attacker could exploit this vulnerability by sending malicious Ethernet frames through an affected device. A successful exploit could allow the attacker do either of the following: Fill the /ngfw partition on the device: A full /ngfw partition could result in administrators being unable to log in to the device (including logging in through the console port) or the device being unable to boot up correctly. Note: Manual intervention is required to recover from this situation. Customers are advised to contact the Cisco Technical Assistance Center (TAC) to help recover a device in this condition. Cause a process crash: The process crash would cause the device to reload. No manual intervention is necessary to recover the device after the reload.

## Affected

- `secure_firewall_threat_defense < 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`
- `secure_firewall_threat_defense >= 6.6.0, < 6.6.1`

## Remediation

Upgrade past the affected range:

- `secure_firewall_threat_defense 6.6.1`