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Vulnerabilities/CVE-2021-43226Public Intelligence Dossier
Source: microsoft · Limited verification•Last verified: •Collection Healthy
CVE-2021-43226ListedHIGH (raw)CVSS 7.8NVD-CWE-noinfo

Windows Common Log File System Driver Elevation of Privilege Vulnerability

Published: 15 Dec 2021•Last updated: 22 Aug 2026, 09:46 AM IST•Source identifier: secure@microsoft.com
Dossier completeness: source-provided sections 3 / 3 · rule guidance available. Missing source facts count as incomplete.
Official source
CISA KEV catalog
Listed
Added06 Oct 2025
Due27 Oct 2025
RansomwareKnown
CVSS score
7.8HIGH (raw)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Metric sourcesecure@microsoft.com
EPSS probability
3.3%0.033
Percentile88th
Weakness type
NVD-CWE-noinfo
No further CWE recorded
Remediation
Patch status unknown
No fixed version or KB recorded

Why It Matters

Analysis dossier

Why It Matters

Windows Common Log File System Driver Elevation of Privilege Vulnerability

SOC priority

Immediate Attention

Actively exploited

Yes

Publicly disclosed

Unknown

Risk basis: CISA KEV exploitation signal; Microsoft or Microsoft-managed product relevance; HIGH severity; Known exploitation signal from CISA KEV or ransomware metadata

Affected Products & Remediation

19 source-backed products
Affected products and versions (source)
  • microsoft windows 10 1507 · < 10.0.10240.19145 · NVD CPE · Source
  • microsoft windows 10 1607 · < 10.0.14393.4825 · NVD CPE · Source
  • microsoft windows 10 1809 · < 10.0.17763.2366 · NVD CPE · Source
  • microsoft windows 10 1909 · < 10.0.18363.1977 · NVD CPE · Source
  • microsoft windows 10 2004 · < 10.0.19041.1415 · NVD CPE · Source
  • microsoft windows 10 20h2 · < 10.0.19042.1415 · NVD CPE · Source
  • microsoft windows 10 21h1 · < 10.0.19043.1415 · NVD CPE · Source
  • microsoft windows 10 21h2 · < 10.0.19044.1415 · NVD CPE · Source
  • microsoft windows 11 21h2 · < 10.0.22000.376 · NVD CPE · Source
  • microsoft windows 7 · version range not provided by source · NVD CPE · Source
  • microsoft windows 8.1 · version range not provided by source · NVD CPE · Source
  • microsoft windows rt 8.1 · version range not provided by source · NVD CPE · Source
  • microsoft windows server 2004 · < 10.0.19041.1415 · NVD CPE · Source
  • microsoft windows server 2008 · r2 · NVD CPE · Source
  • microsoft windows server 2012 · r2 · NVD CPE · Source
  • microsoft windows server 2016 · < 10.0.14393.4825 · NVD CPE · Source
  • microsoft windows server 2019 · < 10.0.17763.2366 · NVD CPE · Source
  • microsoft windows server 2022 · < 10.0.20348.405 · NVD CPE · Source
  • microsoft windows server 20h2 · < 10.0.19042.1415 · NVD CPE · Source
Recorded patch / KBNot provided by source

Vendor or catalog guidance (source)

  • CISA KEV: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Known exploitation (source facts)

Only what a source states. Unknown means no source has said either way; it is not "not exploited".

CISA KEV
Listed
Exploited (source statement)
Yes
Publicly disclosed (source)
Unknown

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.

Suggested hunting (rule-based inference)

SecOps Signal recommendation (rule-based inference). These steps are hunting hypotheses from the vulnerability class; they do not state or imply that exploitation occurred here or anywhere.

Matched microsoft-enterprise (Affected product: microsoft windows 10 1507, Vendor: microsoft); local-privilege-escalation (CVSS AV:L, CVSS PR:L)

Exposure

  1. Identify affected Microsoft products and compare local builds with the MSRC advisory.Telemetry: DeviceTvmSoftwareVulnerabilities · The MSRC product/build mapping establishes applicability. · Rule microsoft-enterprise
  2. Identify hosts reporting this CVE, prioritising shared or multi-user systems.Telemetry: DeviceTvmSoftwareVulnerabilities · A local, low-privilege vector matters most where untrusted users can run code. · Rule local-privilege-escalation

Exploitation evidence

  1. Review the advisory's documented behavior on matching hosts before selecting a hunt.Telemetry: DeviceProcessEvents · Product family alone does not justify a CVE-specific detection. · Rule microsoft-enterprise
Show more (2)

Exploitation evidence

  1. Look for low-privileged processes spawning SYSTEM or root-level child processes on affected hosts.Telemetry: DeviceProcessEvents · Hunting hypothesis from the CVSS vector; privilege transitions are a focused starting point, not evidence of attack. · Rule local-privilege-escalation

Response

  1. Confirm the source-stated KB or mitigation on matching assets.Telemetry: DeviceTvmSoftwareVulnerabilities · A post-update inventory check verifies remediation. · Rule microsoft-enterprise

CISA KEV Record

Catalog entry
06 Oct 2025
Required action due
27 Oct 2025
Known ransomware use
Known

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Change History & Source Data

— No recorded material change

CNA / source
secure@microsoft.com
Record status · verification
UPDATED · Microsoft primary source linked; CISA KEV confirmed
CPE
cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:x64:*, cpe:2.3:o:microsoft:windows_10_1507:*:*:*:*:*:*:x86:*, cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x64:*, cpe:2.3:o:microsoft:windows_10_1607:*:*:*:*:*:*:x86:*, cpe:2.3:o:microsoft:windows_10_1809:*:*:*:*:*:*:*:*, cpe:2.3:o:microsoft:windows_10_1909:*:*:*:*:*:*:*:*, cpe:2.3:o:microsoft:windows_10_2004:*:*:*:*:*:*:*:*, cpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:arm64:*, cpe:2.3:o:microsoft:windows_10_20h2:*:*:*:*:*:*:x86:*, cpe:2.3:o:microsoft:windows_10_21h1:*:*:*:*:*:*:*:*

Evidence & Provenance

4 public sources
CISA KEV CatalogAdded 2025-10-06portal.msrc.microsoft.comSource recordnvd.nist.govSource recordcisa.govSource record

Linked by the query's stored exact CVE association. Review required tables and validation status before use.

Detection Hunting Query
Target: DeviceTvmSoftwareVulnerabilities•Defender XDR
Detect endpoints exposed to CVE-2021-43226
Purpose: Exposure assessment (Category: Exposure Check)Why linked: Query metadata names CVE-2021-43226
DeviceTvmSoftwareVulnerabilities| where CveId == "CVE-2021-43226"| project DeviceId, DeviceName, OSPlatform, OSVersion, SoftwareVendor, SoftwareName, SoftwareVersion, CveId, VulnerabilitySeverityLevel, RecommendedSecurityUpdate, RecommendedSecurityUpdateId| sort by VulnerabilitySeverityLevel desc
Schema Checked · Not runtime validatedSource: SecOps Signal deterministic template · Limited verificationStatic screening: Passed structure and schema checks; tenant execution is not verified.
Open KQL Library
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Correlated briefings

SecOps Signal surfaces public advisory facts only. A missing value means the source has not published it, not that your environment is unaffected. No tenant inventory is connected.