CVE-2025-20333: in the CISA KEV catalogue
Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability. CISA added CVE-2025-20333 to the Known Exploited Vulnerabilities catalogue on 2025-09-25 with a default due date of 2025-09-26. Known ransomware campaign use: Unknown. Forensic triage flag: No.
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. (CISA description)
- Vendor / product
- Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense
- CWE
- CWE-120
- CISA 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 or discontinue use of the product if mitigations are not available.
- EPSS
- 72%, percentile 99 (scored 2026-11-03)
EPSS puts about 72 in 100 odds (72%) on exploitation activity being observed in the next 30 days. Its score is higher than or equal to that of 99% of scored CVEs. This is a model estimate about exploitation anywhere, not about your environment.
Vendor and reference links (from CISA)
- https://www.cisa.gov/news-events/directives/ed-25-03-identify-and-mitigate-potential-compromise-cisco-devices
- 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
Your own deadline under CISA BOD 26-04 depends on exposure, automatability and technical impact: work it out with the BOD 26-04 calculator.
Frequently asked questions
Is CVE-2025-20333 in the CISA KEV catalogue?
Yes. CISA added CVE-2025-20333 (Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability) to the Known Exploited Vulnerabilities catalogue on 2025-09-25. CISA's default due date for it is 2025-09-26.
Is CVE-2025-20333 used in ransomware attacks?
CISA marks known ransomware campaign use as Unknown for CVE-2025-20333. That means CISA lacks confirmation, not that ransomware groups do not use it.
What should I do about 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 or discontinue use of the product if mitigations are not available.
Sources
- CISA, Known Exploited Vulnerabilities Catalog (accessed 2026-11-03)
- FIRST, Exploit Prediction Scoring System (EPSS) (EPSS by FIRST; scores generated by Empirical Security)
- NVD record for CVE-2025-20333