---
id: "CVE-2021-43226"
kind: "vulnerability"
aliases: ["CVE-2021-43226"]
title: "Windows Common Log File System Driver 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 1507", "fixed": ["10.0.10240.19145"], "affected": "< 10.0.10240.19145", "ecosystem": "vendor"}, {"name": "microsoft windows 10 1607", "fixed": ["10.0.14393.4825"], "affected": "< 10.0.14393.4825", "ecosystem": "vendor"}, {"name": "microsoft windows 10 1809", "fixed": ["10.0.17763.2366"], "affected": "< 10.0.17763.2366", "ecosystem": "vendor"}, {"name": "microsoft windows 10 1909", "fixed": ["10.0.18363.1977"], "affected": "< 10.0.18363.1977", "ecosystem": "vendor"}, {"name": "microsoft windows 10 2004", "fixed": ["10.0.19041.1415"], "affected": "< 10.0.19041.1415", "ecosystem": "vendor"}, {"name": "microsoft windows 10 20h2", "fixed": ["10.0.19042.1415"], "affected": "< 10.0.19042.1415", "ecosystem": "vendor"}, {"name": "microsoft windows 10 21h1", "fixed": ["10.0.19043.1415"], "affected": "< 10.0.19043.1415", "ecosystem": "vendor"}, {"name": "microsoft windows 10 21h2", "fixed": ["10.0.19044.1415"], "affected": "< 10.0.19044.1415", "ecosystem": "vendor"}, {"name": "microsoft windows 11 21h2", "fixed": ["10.0.22000.376"], "affected": "< 10.0.22000.376", "ecosystem": "vendor"}, {"name": "microsoft windows 7", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft windows 8.1", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft windows rt 8.1", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "microsoft windows server 2004", "fixed": ["10.0.19041.1415"], "affected": "< 10.0.19041.1415", "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": ["10.0.14393.4825"], "affected": "< 10.0.14393.4825", "ecosystem": "vendor"}, {"name": "microsoft windows server 2019", "fixed": ["10.0.17763.2366"], "affected": "< 10.0.17763.2366", "ecosystem": "vendor"}, {"name": "microsoft windows server 2022", "fixed": ["10.0.20348.405"], "affected": "< 10.0.20348.405", "ecosystem": "vendor"}, {"name": "microsoft windows server 20h2", "fixed": ["10.0.19042.1415"], "affected": "< 10.0.19042.1415", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "infrastructure", "ransomware", "self-hosted", "windows"]
not_affected_if: ["patched-systems"]
published_at: "2021-12-15T15:15:09+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-23T23:44:51+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-43226", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-43226", "first_seen_at": "2026-10-23T23:44:51+00:00"}]
---

# Windows Common Log File System Driver Elevation of Privilege Vulnerability

Windows Common Log File System (CLFS) driver has a privilege escalation flaw that lets a local user with some access gain higher privileges. CISA lists it as actively exploited, with ransomware use noted in the catalog.

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

## Affected

- vendor:Microsoft Windows affected ? fixed ?
- vendor:microsoft windows 10 1507 affected < 10.0.10240.19145 fixed 10.0.10240.19145
- vendor:microsoft windows 10 1607 affected < 10.0.14393.4825 fixed 10.0.14393.4825
- vendor:microsoft windows 10 1809 affected < 10.0.17763.2366 fixed 10.0.17763.2366
- vendor:microsoft windows 10 1909 affected < 10.0.18363.1977 fixed 10.0.18363.1977
- vendor:microsoft windows 10 2004 affected < 10.0.19041.1415 fixed 10.0.19041.1415
- vendor:microsoft windows 10 20h2 affected < 10.0.19042.1415 fixed 10.0.19042.1415
- vendor:microsoft windows 10 21h1 affected < 10.0.19043.1415 fixed 10.0.19043.1415
- vendor:microsoft windows 10 21h2 affected < 10.0.19044.1415 fixed 10.0.19044.1415
- vendor:microsoft windows 11 21h2 affected < 10.0.22000.376 fixed 10.0.22000.376
- vendor:microsoft windows 7 affected ? fixed ?
- vendor:microsoft windows 8.1 affected ? fixed ?
- vendor:microsoft windows rt 8.1 affected ? fixed ?
- vendor:microsoft windows server 2004 affected < 10.0.19041.1415 fixed 10.0.19041.1415
- 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 < 10.0.14393.4825 fixed 10.0.14393.4825
- vendor:microsoft windows server 2019 affected < 10.0.17763.2366 fixed 10.0.17763.2366
- vendor:microsoft windows server 2022 affected < 10.0.20348.405 fixed 10.0.20348.405
- vendor:microsoft windows server 20h2 affected < 10.0.19042.1415 fixed 10.0.19042.1415

## Fix

Apply the Microsoft patch for CVE-2021-43226 per vendor instructions; the sources do not name the KB or build numbers.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-43226
- 2026-10-23T23:44:51+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-43226

## From the sources

Microsoft Windows Common Log File System Driver contains a privilege escalation vulnerability that could allow a local, privileged attacker to bypass certain security mechanisms.

CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, 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_