CVE-2025-21418: Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 11 Feb 2025, the same day the CVE record was published.

How likely is exploitation in the next 30 days?

2.1%

EPSS score, percentile 81.9 of all scored records

How severe?

7.8 High

CVSS v3.1 base score, given by the CNA

What should I do?

Required action (CISA), due 4 Mar 2025: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Advisories and patches (1)

Which versions are affected?

Affected: 10.0.10240.0 up to, not including, 10.0.10240.20915; 10.0.14393.0 up to, not including, 10.0.14393.7785; 10.0.17763.0 up to, not including, 10.0.17763.6893; 10.0.19044.0 up to, not including, 10.0.19044.5487; 10.0.19045.0 up to, not including, 10.0.19045.5487; 10.0.22621.0 up to, not including, 10.0.22621.4890; 10.0.22631.0 up to, not including, 10.0.22631.4890; 10.0.22631.0 up to, not including, 10.0.22631.4890; 10.0.26100.0 up to, not including, 10.0.26100.3194; 6.1.7601.0 up to, not including, 6.1.7601.27566; 6.1.7601.0 up to, not including, 6.1.7601.27566; 6.0.6003.0 up to, not including, 6.0.6003.23117; 6.0.6003.0 up to, not including, 6.0.6003.23117; 6.2.9200.0 up to, not including, 6.2.9200.25317; 6.2.9200.0 up to, not including, 6.2.9200.25317; 6.3.9600.0 up to, not including, 6.3.9600.22417; 6.3.9600.0 up to, not including, 6.3.9600.22417; 10.0.14393.0 up to, not including, 10.0.14393.7785; 10.0.14393.0 up to, not including, 10.0.14393.7785; 10.0.17763.0 up to, not including, 10.0.17763.6893

Versions by product

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

CISA due date for this action: 4 March 2025.

Advisories and patches

• Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability (Vendor advisory, Patch)

Linked from CISA's catalog entry

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21418
• https://nvd.nist.gov/vuln/detail/CVE-2025-21418

Affected products and versions

As listed 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

Microsoft Windows Ancillary Function Driver for WinSock contains a heap-based buffer overflow vulnerability that allows for privilege escalation, enabling a local attacker to gain SYSTEM privileges.

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2025-21418 to its Known Exploited Vulnerabilities (KEV) catalog on 11 Feb 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 4 Mar 2025.
• The CVE record was published on 11 Feb 2025, the same day it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 7.8 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 2.1% (percentile 81.9), 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

Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Weakness

• CWE-122: Heap-based Buffer Overflow

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

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