CVE-2025-20333: Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability

How to check if you are exposed to CVE-2025-20333

1. Find every Cisco Secure Firewall Adaptive Security Appliance and Secure Firewall Threat Defense system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
2. Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
3. Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2025-20333.

US federal agencies had to fix this by 2025-09-26. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Affected versions

Versions the National Vulnerability Database lists as vulnerable to CVE-2025-20333. Check the vendor advisory for the exact fixed builds before you sign anything off.

Timeline

1. 2025-09-25 · Published in the National Vulnerability Database
2. 2025-09-25 · Added to CISA's Known Exploited Vulnerabilities catalog, the same day it was published
3. 2025-09-26 · Fix-by date for US federal agencies, passed 401 days ago

Vendor advisories and fixes

• 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

Weakness type

• CWE-120

More exploited Cisco vulnerabilities

CISA lists 102 exploited Cisco vulnerabilities. The closest matches:

• CVE-2025-20362Cisco Secure Firewall Adaptive Security (ASA) Appliance and Secure Firewall Threat Defense (FTD) Missing Authorization VulnerabilityAdded 2025-09-25
• CVE-2026-76418Cisco Secure Firewall ASA Software and Cisco Secure FTD Software Unchecked Return Value to NULL Pointer Dereference VulnerabilityAdded 2026-10-29
• CVE-2026-76519Cisco Secure Email Gateway Relative Path Traversal VulnerabilityAdded 2026-10-14
• CVE-2026-76504Cisco Catalyst SD-WAN Manager Hex Encoding VulnerabilityAdded 2026-09-30
• CVE-2026-76460Cisco Identity Services Engine Incorrect Use of Privileged APIs VulnerabilityAdded 2026-09-16
• CVE-2026-76461Cisco Secure Email Gateway SQL Injection VulnerabilityAdded 2026-09-14
• CVE-2026-20079Cisco Firewall Management Center Authentication Bypass Using an Alternate Path or Channel VulnerabilityAdded 2026-09-09
• CVE-2026-20349Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Heap Inspection VulnerabilityAdded 2026-08-11

Keep going

• All exploited CVEs
• Check another CVE
• What is CISA KEV?
• What is EPSS?

Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.