---
id: "CVE-2025-21418"
kind: "vulnerability"
aliases: ["CVE-2025-21418"]
title: "Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability"
severity: "high"
cvss: 7.8
epss: null
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Microsoft Windows", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft windows 10 1607", "fixed": ["10.0.10240.20915"], "affected": "< 10.0.10240.20915", "ecosystem": "vendor"}, {"name": "microsoft windows 10 1809", "fixed": ["10.0.17763.6893"], "affected": "< 10.0.17763.6893", "ecosystem": "vendor"}, {"name": "microsoft windows 10 21h2", "fixed": ["10.0.19044.5487"], "affected": "< 10.0.19044.5487", "ecosystem": "vendor"}, {"name": "microsoft windows 10 22h2", "fixed": ["10.0.19045.5487"], "affected": "< 10.0.19045.5487", "ecosystem": "vendor"}, {"name": "microsoft windows 11 22h2", "fixed": ["10.0.22621.4890"], "affected": "< 10.0.22621.4890", "ecosystem": "vendor"}, {"name": "microsoft windows 11 23h2", "fixed": ["10.0.22631.4890"], "affected": "< 10.0.22631.4890", "ecosystem": "vendor"}, {"name": "microsoft windows 11 24h2", "fixed": ["10.0.26100.3107"], "affected": "< 10.0.26100.3107", "ecosystem": "vendor"}, {"name": "microsoft windows server 2008", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft windows server 2008", "fixed": [], "affected": "= r2", "ecosystem": "vendor"}, {"name": "microsoft windows server 2012", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft windows server 2012", "fixed": [], "affected": "= r2", "ecosystem": "vendor"}, {"name": "microsoft windows server 2016", "fixed": ["10.0.14393.7785"], "affected": "< 10.0.14393.7785", "ecosystem": "vendor"}, {"name": "microsoft windows server 2019", "fixed": ["10.0.17763.6893"], "affected": "< 10.0.17763.6893", "ecosystem": "vendor"}, {"name": "microsoft windows server 2022", "fixed": ["10.0.20348.3148"], "affected": "< 10.0.20348.3148", "ecosystem": "vendor"}, {"name": "microsoft windows server 2022 23h2", "fixed": ["10.0.25398.1425"], "affected": "< 10.0.25398.1425", "ecosystem": "vendor"}, {"name": "microsoft windows server 2025", "fixed": ["10.0.26100.3107"], "affected": "< 10.0.26100.3107", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "infrastructure", "self-hosted", "windows"]
not_affected_if: ["patched-windows"]
published_at: "2025-02-11T00:00:00+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-23T22:29:05+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2025-21418", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-21418", "first_seen_at": "2026-10-23T22:29:05+00:00"}]
---

# Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

A heap-based buffer overflow in the Windows Ancillary Function Driver for WinSock (afd.sys) lets a local user escalate privileges. An attacker with a local foothold gets SYSTEM privileges, and CISA lists it as exploited in the wild.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Microsoft Windows affected ? fixed ?
- vendor:microsoft windows 10 1607 affected < 10.0.10240.20915 fixed 10.0.10240.20915
- vendor:microsoft windows 10 1809 affected < 10.0.17763.6893 fixed 10.0.17763.6893
- vendor:microsoft windows 10 21h2 affected < 10.0.19044.5487 fixed 10.0.19044.5487
- vendor:microsoft windows 10 22h2 affected < 10.0.19045.5487 fixed 10.0.19045.5487
- vendor:microsoft windows 11 22h2 affected < 10.0.22621.4890 fixed 10.0.22621.4890
- vendor:microsoft windows 11 23h2 affected < 10.0.22631.4890 fixed 10.0.22631.4890
- vendor:microsoft windows 11 24h2 affected < 10.0.26100.3107 fixed 10.0.26100.3107
- vendor:microsoft windows server 2008 affected ? fixed ?
- vendor:microsoft windows server 2008 affected = r2 fixed ?
- vendor:microsoft windows server 2012 affected ? fixed ?
- vendor:microsoft windows server 2012 affected = r2 fixed ?
- vendor:microsoft windows server 2016 affected < 10.0.14393.7785 fixed 10.0.14393.7785
- vendor:microsoft windows server 2019 affected < 10.0.17763.6893 fixed 10.0.17763.6893
- vendor:microsoft windows server 2022 affected < 10.0.20348.3148 fixed 10.0.20348.3148
- vendor:microsoft windows server 2022 23h2 affected < 10.0.25398.1425 fixed 10.0.25398.1425
- vendor:microsoft windows server 2025 affected < 10.0.26100.3107 fixed 10.0.26100.3107

## Fix

Apply the Microsoft security update for CVE-2025-21418 (Windows Ancillary Function Driver for WinSock); the specific KB and affected builds are not in the sources.
CISA says to apply the vendor mitigations or discontinue use of unpatched products.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2025-21418
- 2026-10-23T22:29:05+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2025-21418

## From the sources

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 required action: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_