CVE-2021-43226: Microsoft Windows Privilege Escalation Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 6 Oct 2025, 1,391 days after the CVE record was published.

How likely is exploitation in the next 30 days?

3.3%

EPSS score, percentile 88.4 of all scored records

How severe?

7.8 High

CVSS v3.1 base score, given by the CNA

What should I do?

CISA deadline 27 Oct 2025. Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

The CVE record links no vendor advisory, patch or mitigation.

Which versions are affected?

Affected

• from 10.0.0 to before 10.0.17763.2366
• from 10.0.0 to before 10.0.17763.2366
• from 10.0.0 to before 10.0.17763.2366
• from 10.0.0 to before 10.0.18363.1977
• from 10.0.0 to before 10.0.19043.1415
• from 10.0.0 to before 10.0.20348.405

and 14 more in the table below

Versions by product

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

What to do

CISA due date for this action: 27 October 2025.

Advisories and patches

The CVE record links no vendor advisory, patch or mitigation.

Linked from CISA's catalog entry

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-43226
• https://nvd.nist.gov/vuln/detail/CVE-2021-43226

Affected products and versions

As listed in the CVE record.

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

About this vulnerability

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

Summary: CISA's KEV catalog, as of 28 Oct 2026.

• CISA added CVE-2021-43226 to its Known Exploited Vulnerabilities (KEV) catalog on 6 Oct 2025.
• CISA marks it as known to be used in ransomware campaigns.
• The due date CISA sets for the required action is 27 Oct 2025.
• The CVE record was published on 15 Dec 2021, 1,391 days before it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 7.8 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 3.3% (percentile 88.4), as of 28 Oct 2026.
• CISA's SSVC assessment in the CVE record: exploitation active, automatable no, technical impact total.

Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.

Description

Windows Common Log File System Driver Elevation of Privilege Vulnerability

Windows Common Log File System Driver Elevation of Privilege Vulnerability

Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.

Timeline

References

• portal.msrc.microsoft.com

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