Known exploited · Cisco
CVE-2025-20333: Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability
What it is
Cisco Secure Firewall Adaptive Security (ASA) Appliance and Secure Firewall Threat Defense (FTD) Software VPN Web Server contain a buffer overflow vulnerability that allows for remote code execution. This vulnerability could be chained with CVE-2025-20362.
- Vendor
- Cisco
- Product
- Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense
- Added to KEV
- September 25, 2025
- CISA due date
- September 26, 2025
- Ransomware use
- Unknown
What CISA requires
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 or discontinue use of the product if mitigations are not available.
Forensic triage
No
What to do now
- Find every instance of Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense you run, including the forgotten ones, and check its version against the vendor advisory.
- Apply the vendor's fix or mitigation, before September 26, 2025 if you are bound by CISA's deadline, sooner if it faces the internet.
- Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.
References
- https://www.cisa.gov/news-events/directives/supplemental-direction-ed-25-03-core-dump-and-hunt-instructions
- https://www.cisa.gov/eviction-strategies-tool/create-from-template
- https://sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks
- https://sec.cloudapps.cisco.com/security/center/private/resources/asa_ftd_continued_attacks#Details
- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-webvpn-z5xP8EUB
- https://nvd.nist.gov/vuln/detail/CVE-2025-20333
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Start freeSource: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.