CVE-2025-20333: Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability
Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.
Generated by VEDAS. Scores as of 2026-11-01 19:19 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.
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.
Description quoted from the CVE record (assigned by cisco, published 2025-09-25).
Weakness: Buffer Copy without Checking Size of Input (‘Classic Buffer Overflow’)
How it can be exploited
Exploitable over the network with low attack complexity needing low privileges and no user interaction. Impact: confidentiality high, integrity high, availability high. CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: no. Technical impact: total.
- On CISA KEV since
- 2025-09-25
- US federal deadline
- 2025-09-26
- Ransomware use
- Not known
Public exploit evidence (Exploit Observer)
Also known as: BDU:2025-11706, CNNVD-202509-3956, EUVD-2025-31139, EUVD-2025-31140, GHSA-vg93-6w2x-3cvp
VEDAS cluster: VEDAS:GAUGEGRUNT
Exploit Observer links 4 pieces of public exploit code or detection modules that name this CVE or one of its aliases.
Exploit code and modules (4)
Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.
- Code repository: https://github.com/callinston/cve-2025-20333
- Code repository: https://github.com/callinston/cve-2025-20333-exp
- Code repository: https://github.com/cobbbex/cve-2025-20333
- Code repository: https://github.com/curtishoughton/cisco-asa-cve-2025-20333-scanner
Research and write-ups (2)
- Research or write-up: https://ptsecurity.com/ru-ru/research/trending-vulnerabilities/CVE-2025-20333
- Research or write-up: https://www.ptsecurity.com/research/trending-vulnerabilities/CVE-2025-20333
Vulnerability databases and vendor advisories (7)
Catalogue entries, not exploit evidence.
- Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2025-31139
- Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2025-31140
- Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-vg93-6w2x-3cvp
- Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2025-20333
- Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-20333
- Vulnerability database or vendor advisory: https://www.cnnvd.org.cn/home/globalSearch?keyword=CNNVD-202509-3956
- Vulnerability database or vendor advisory: https://www.tenable.com/cve/CVE-2025-20333
57 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.
VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.
Live scores
- EPSS
- 0.712
very likely to be attacked soon - VEDAS
- 0.982
strong exploit evidence - On CISA KEV
- Yes, since 2025-09-25
- Detection rule
- None yet
Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish.
Who is affected
| Product | Affected | Not affected |
|---|---|---|
| Cisco Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | version 9.8.1 version 9.8.1.5 version 9.8.1.7 version 9.8.2 version 9.8.2.8 version 9.8.2.14 version 9.8.2.15 version 9.8.2.17 and 198 more ranges | Not stated |
| Cisco Cisco Secure Firewall Threat Defense (FTD) Software | version 6.2.3 version 6.2.3.1 version 6.2.3.2 version 6.2.3.3 version 6.2.3.4 version 6.2.3.5 version 6.2.3.6 version 6.2.3.7 and 86 more ranges | Not stated |
Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.
Exploit Observer also maps it to: cisco adaptive_security_appliance_software, cisco secure_firewall_threat_defense, cisco_systems,_inc. adaptive_security_appliance.
How to fix it
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.
Vendor guidance:
- https://sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks (vendor-advisory)
How to detect it
There is no open VEDAS detection rule for this bug yet. It is listed on the detection gaps page if CISA has confirmed attacks.
Advisories on this CVE
References
Vendor advisories and patches
- https://sec.cloudapps.cisco.com/security/center/resources/asa_ftd_continued_attacks (vendor-advisory)
Government sources
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-20333 (government-resource)
Other references
Other databases
Where this comes from
This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.