CVE-2025-20333: Cisco Secure Firewall Adaptive Security Appliance (ASA) and Secure Firewall Threat Defense (FTD) Buffer Overflow Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 25 Sep 2025, the same day the CVE record was published.
- How likely is exploitation in the next 30 days?
- 71.2%
EPSS score, percentile 99.4 of all scored records
- How severe?
- 9.9 Critical
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA deadline 26 Sep 2025. 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 … Full text
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- 9.8.1
- 9.8.1.5
- 9.8.1.7
- 9.8.2
- 9.8.2.8
- 9.8.2.14
and 18 more in the table below
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
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.
CISA due date for this action: 26 September 2025.
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
Linked from CISA's catalog entry
- 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
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | 9.8.1 |
| Affected | 9.8.1.5 |
| Affected | 9.8.1.7 |
| Affected | 9.8.2 |
| Affected | 9.8.2.8 |
| Affected | 9.8.2.14 |
| Affected | 9.8.2.15 |
| Affected | 9.8.2.17 |
| Affected | 9.8.2.20 |
| Affected | 9.8.2.24 |
| Affected | 9.8.2.26 |
| Affected | 9.8.2.28 |
And 194 more version entries in the CVE record.
| Status | Versions |
|---|---|
| Affected | 6.2.3 |
| Affected | 6.2.3.1 |
| Affected | 6.2.3.2 |
| Affected | 6.2.3.3 |
| Affected | 6.2.3.4 |
| Affected | 6.2.3.5 |
| Affected | 6.2.3.6 |
| Affected | 6.2.3.7 |
| Affected | 6.2.3.8 |
| Affected | 6.2.3.10 |
| Affected | 6.2.3.11 |
| Affected | 6.2.3.9 |
And 82 more version entries in the CVE record.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this vulnerability
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.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2025-20333 to its Known Exploited Vulnerabilities (KEV) catalog on 25 Sep 2025.
- CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
- The due date CISA sets for the required action is 26 Sep 2025.
- The CVE record was published on 25 Sep 2025, the same day it was added to KEV.
- The CVE record carries a CVSS v3.1 base score of 9.9 (Critical), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 71.2% (percentile 99.4), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
Description
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.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 25 Sep 2025 | CVE record published |
| 25 Sep 2025 | Added to CISA KEV |
| 26 Sep 2025 | CISA due date for the required action |
| 26 Feb 2026 | CVE record last updated |
References
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