Known exploited vulnerability
CVE-2025-20333
The short answer
CVE-2025-20333 affects Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and is rated critical (CVSS 9.9). CISA added it to the Known Exploited Vulnerabilities catalog on 2025-09-25: attackers are using it, so patch it first.
What it is
A vulnerability in the VPN web server of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to execute arbitrary code on an affected device. This vulnerability is due to improper validation of user-supplied input in HTTP(S) requests. An attacker with valid VPN user credentials could exploit this vulnerability by sending crafted HTTP requests to an affected device. A successful exploit could allow the attacker to execute arbitrary code as root, possibly resulting in the complete compromise of the affected device.
Weakness: CWE-120.
Severity
9.9 critical
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Exploited (CISA KEV)
Yes, since Sep 25, 2025
Federal due date Sep 26, 2025
EPSS, next 30 days
72%
Higher than 99% of scored CVEs
How it can be exploited
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
What CISA says to do
The KEV due date refers to the deadline by which FCEB agencies are expected to review and begin implementing the guidance outlined in Emergency Directive (ED) 25-03 (URL listed below in Notes). Agencies must follow the mitigation steps provided by CISA (URL listed below in Notes) and vendor’s instructions (URL listed below in Notes). Adhere to the applicable BOD 22-01 guidance for cloud services…
Affected products
Cisco Secure Firewall Adaptive Security Appliance (ASA) Software, Cisco Secure Firewall Threat Defense (FTD) Software. NVD's record lists the exact affected versions.
References
- sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-z5xP8EUB Vendor Advisory
- sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks Vendor Advisory
- www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-20333 US Government Resource
Questions
Is CVE-2025-20333 being exploited?
Yes. CISA added CVE-2025-20333 to its Known Exploited Vulnerabilities catalog on 2025-09-25, with a federal remediation due date of 2025-09-26.
How do I fix CVE-2025-20333?
CISA's required action: The KEV due date refers to the deadline by which FCEB agencies are expected to review and begin implementing the guidance outlined in Emergency Directive (ED) 25-03 (URL listed below in Notes). Agencies must follow the mitigation steps provided by CISA (URL listed below in Notes) and vendor’s instructions (URL listed below in Notes). Adhere to the applicable BOD 22-01 guidance for cloud services…
From NVD, CISA KEV, FIRST EPSS and OSV.dev, checked . Status on NVD: Analyzed. The description is NVD's text, quoted as published.
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