---
title: "CVE-2025-21418: Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability"
url: https://erroneo.us/security/cve/CVE-2025-21418/
description: "CVE-2025-21418 (Microsoft Windows): Exploited in the wild (CISA KEV). Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability"
type: vulnerability-record
section: "Security Digest"
date_published: 2025-02-11
date_modified: 2026-02-26
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2025-21418"
kev: true
cvss: 7.8
epss: 0.01568
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Microsoft Windows. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-02-11, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-03-04 ; treat that as the outer limit, not the target.
- EPSS 1.6% , percentile 75: FIRST’s model estimates a 1.6% chance of exploitation activity in the next 30 days, higher than 75% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Needs local access needed. Lower urgency for most teams unless an attacker could already run code on the machine.

## What it is

Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

## Affected products (CVE record)

- Microsoft Windows 10 Version 1507: 10.0.10240.0 < 10.0.10240.20915
- Microsoft Windows 10 Version 1607: 10.0.14393.0 < 10.0.14393.7785
- Microsoft Windows 10 Version 1809: 10.0.17763.0 < 10.0.17763.6893
- Microsoft Windows 10 Version 21H2: 10.0.19044.0 < 10.0.19044.5487
- Microsoft Windows 10 Version 22H2: 10.0.19045.0 < 10.0.19045.5487
- Microsoft Windows 11 version 22H2: 10.0.22621.0 < 10.0.22621.4890
- Microsoft Windows 11 version 22H3: 10.0.22631.0 < 10.0.22631.4890
- Microsoft Windows 11 Version 23H2: 10.0.22631.0 < 10.0.22631.4890
- Microsoft Windows 11 Version 24H2: 10.0.26100.0 < 10.0.26100.3194
- Microsoft Windows Server 2008 R2 Service Pack 1: 6.1.7601.0 < 6.1.7601.27566

## Severity

- microsoft CVSS 3.1: 7.8 `CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C`

## Exploitation

- CISA KEV: added 2025-02-11; federal due date 2025-03-04. Known ransomware use: Unknown.
- CISA required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
- CISA SSVC assessment: exploitation active , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 1.57% probability of exploitation activity in the next 30 days; percentile 75.

## Sources

- [Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21418)
- [CVE.org record CVE-2025-21418](https://www.cve.org/CVERecord?id=CVE-2025-21418)
- [NVD entry CVE-2025-21418](https://nvd.nist.gov/vuln/detail/CVE-2025-21418)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21418)

---
Source page: https://erroneo.us/security/cve/CVE-2025-21418/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt