---
id: CVE-2020-3561
title: >-
  A vulnerability in the Clientless SSL VPN (WebVPN) of Cisco Adaptive Security
  Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
  could allow an unauthenticated, remote attacker to inject arbitrary HTTP
  headers in …
summary: >-
  A vulnerability in the Clientless SSL VPN (WebVPN) of Cisco Adaptive Security
  Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software
  could allow an unauthenticated, remote attacker to inject arbitrary HTTP
  headers in …
severity: medium
cvss: 4.7
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N'
cwe:
  - CWE-93
  - CWE-74
vendor: cisco
product: adaptive_security_appliance
affected:
  - adaptive_security_appliance < 9.6.4.35
  - 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'
  - 'adaptive_security_appliance_software >= 9.8.0, < 9.8.4.20'
  - 'adaptive_security_appliance_software >= 9.9.0, < 9.9.2.80'
  - 'adaptive_security_appliance_software >= 9.10.0, < 9.10.1.43'
  - 'adaptive_security_appliance_software >= 9.12.0, < 9.12.3.9'
  - 'adaptive_security_appliance_software >= 9.13.0, < 9.13.1.10'
  - 'adaptive_security_appliance_software >= 9.14.0, < 9.14.1.10'
patched:
  - adaptive_security_appliance 9.6.4.35
  - secure_firewall_threat_defense 6.6.1
  - adaptive_security_appliance_software 9.14.1.10
published: '2020-10-21'
updated: '2026-08-11'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2020-3561'
references:
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-crlf-inj-BX9uRwSn
    label: psirt@cisco.com
  - url: >-
      https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-crlf-inj-BX9uRwSn
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.0128
epssPercentile: 0.68725
ingestedAt: '2026-08-11T19:48:28.843Z'
---

## Overview

A vulnerability in the Clientless SSL VPN (WebVPN) of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to inject arbitrary HTTP headers in the responses of the affected system. The vulnerability is due to improper input sanitization. An attacker could exploit this vulnerability by persuading a user of the interface to click a crafted link. A successful exploit could allow the attacker to conduct a CRLF injection attack, adding arbitrary HTTP headers in the responses of the system and redirecting the user to arbitrary websites.

## Affected

- `adaptive_security_appliance < 9.6.4.35`
- `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`
- `adaptive_security_appliance_software >= 9.8.0, < 9.8.4.20`
- `adaptive_security_appliance_software >= 9.9.0, < 9.9.2.80`
- `adaptive_security_appliance_software >= 9.10.0, < 9.10.1.43`
- `adaptive_security_appliance_software >= 9.12.0, < 9.12.3.9`
- `adaptive_security_appliance_software >= 9.13.0, < 9.13.1.10`
- `adaptive_security_appliance_software >= 9.14.0, < 9.14.1.10`

## Remediation

Upgrade past the affected range:

- `adaptive_security_appliance 9.6.4.35`
- `secure_firewall_threat_defense 6.6.1`
- `adaptive_security_appliance_software 9.14.1.10`