CVEs / CVE-2025-21418

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

Known exploited in the CISA KEV catalog since 11 Feb 2025
high 7.8 CVSS 3.1 (from the CNA)
EPSS 2.13% chance of exploitation in the next 30 days, higher than 81% of CVEs (30 Oct 2026)
Last changed at its sources 17 Jun 2026

Are you affected? Check your servers with Stackurity: it lists the software on each server and the vulnerabilities to fix first.

Check your servers with Stackurity Already using Stackurity? Search for CVE-2025-21418

Summary

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.
CISA, Known Exploited Vulnerabilities catalog

Description

Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability
The CVE record, via NVD · published 11 Feb 2025 · NVD status: Analyzed

Affected and fixed versions

As stated by the CVE record (from the CNA)
Product	Affected	Fixed in
Microsoft Windows 10 Version 1507	from 10.0.10240.0, before 10.0.10240.20915	10.0.10240.20915
Microsoft Windows 10 Version 1607	from 10.0.14393.0, before 10.0.14393.7785	10.0.14393.7785
Microsoft Windows 10 Version 1809	from 10.0.17763.0, before 10.0.17763.6893	10.0.17763.6893
Microsoft Windows 10 Version 21H2	from 10.0.19044.0, before 10.0.19044.5487	10.0.19044.5487
Microsoft Windows 10 Version 22H2	from 10.0.19045.0, before 10.0.19045.5487	10.0.19045.5487
Microsoft Windows 11 version 22H2	from 10.0.22621.0, before 10.0.22621.4890	10.0.22621.4890
Microsoft Windows 11 version 22H3	from 10.0.22631.0, before 10.0.22631.4890	10.0.22631.4890
Microsoft Windows 11 Version 23H2	from 10.0.22631.0, before 10.0.22631.4890	10.0.22631.4890
Microsoft Windows 11 Version 24H2	from 10.0.26100.0, before 10.0.26100.3194	10.0.26100.3194
Microsoft Windows Server 2008 R2 Service Pack 1	from 6.1.7601.0, before 6.1.7601.27566	6.1.7601.27566
Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation)	from 6.1.7601.0, before 6.1.7601.27566	6.1.7601.27566
Microsoft Windows Server 2008 Service Pack 2	from 6.0.6003.0, before 6.0.6003.23117	6.0.6003.23117
Microsoft Windows Server 2008 Service Pack 2 (Server Core installation)	from 6.0.6003.0, before 6.0.6003.23117	6.0.6003.23117
Microsoft Windows Server 2012	from 6.2.9200.0, before 6.2.9200.25317	6.2.9200.25317
Microsoft Windows Server 2012 (Server Core installation)	from 6.2.9200.0, before 6.2.9200.25317	6.2.9200.25317
Microsoft Windows Server 2012 R2	from 6.3.9600.0, before 6.3.9600.22417	6.3.9600.22417
Microsoft Windows Server 2012 R2 (Server Core installation)	from 6.3.9600.0, before 6.3.9600.22417	6.3.9600.22417
Microsoft Windows Server 2016	from 10.0.14393.0, before 10.0.14393.7785	10.0.14393.7785
Microsoft Windows Server 2016 (Server Core installation)	from 10.0.14393.0, before 10.0.14393.7785	10.0.14393.7785
Microsoft Windows Server 2019	from 10.0.17763.0, before 10.0.17763.6893	10.0.17763.6893
Microsoft Windows Server 2019 (Server Core installation)	from 10.0.17763.0, before 10.0.17763.6893	10.0.17763.6893
Microsoft Windows Server 2022	from 10.0.20348.0, before 10.0.20348.3207	10.0.20348.3207
Microsoft Windows Server 2022, 23H2 Edition (Server Core installation)	from 10.0.25398.0, before 10.0.25398.1425	10.0.25398.1425
Microsoft Windows Server 2025	from 10.0.26100.0, before 10.0.26100.3194	10.0.26100.3194
Microsoft Windows Server 2025 (Server Core installation)	from 10.0.26100.0, before 10.0.26100.3194	10.0.26100.3194

Exploitation

In CISA KEV since	11 Feb 2025
Due date for US federal agencies	4 Mar 2025
Used in ransomware campaigns	Unknown
Required action	Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Severity

CVSS 3.1	7.8 high `CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H` Scored by the CNA ([email protected])
Weakness	CWE-122

References

CVE-2025-21418 on NVD
CVE-2025-21418 in the CISA KEV catalog
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21418 (cited by CISA)
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21418 Patch, Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21418 US Government Resource

Sources

Exploitation status from the CISA Known Exploited Vulnerabilities catalog. EPSS scores from FIRST. Descriptions, severity and references from the National Vulnerability Database. Open-source package versions from OSV (CC-BY 4.0). Text is shown as each source states it; Stackurity does not edit it. Check the vendor's advisory before acting.

This product uses data from the NVD API but is not endorsed or certified by the NVD.