CVE-2020-3561
Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN CRLF Injection Vulnerability
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- Required
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
4.7
Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN CRLF Injection Vulnerability
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.
- Record
CVE-2020-3561- CVSS 3.0
- 4.7 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N - Weakness
- CWE-93
- Updated
- 2026-11-02
EUVDEUVD-2020-24832
4.7
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.
- Record
EUVD-2020-24832- CVSS 3.0
- 4.7 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N - Updated
- 2026-11-03
GitHub AdvisoriesGHSA-pm23-qjx3-gg3f
4.7
A vulnerability in the Clientless SSL VPN (WebVPN) of Cisco Adaptive Security Appliance (ASA)...
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.
- Record
GHSA-pm23-qjx3-gg3f- CVSS 3.1
- 4.7 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N - Weakness
- CWE-74, CWE-93
- Updated
- 2026-11-02
NVD
4.7
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.
- Record
CVE-2020-3561- CVSS 3.1
- 4.7 Medium
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N - CVSS 3.0
- 4.7 Medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N - CVSS 2.0
- 4.3 Medium
AV:N/AC:M/Au:N/C:N/I:P/A:N - Weakness
- CWE-93, CWE-74
- Updated
- 2026-11-02
Affected products
History
| Recorded | Changed | Sources |
|---|---|---|
| facts | ||
| aliases, published | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2020-3561 is a medium vulnerability (CVSS 4.7) in Cisco Adaptive Security Appliance, published October 21, 2020. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.27%, the 70th percentile. No source names a fixed version.