CVE-2021-40450: Microsoft Win32k Privilege Escalation Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 25 Apr 2022, 194 days after the CVE record was published.

How likely is exploitation in the next 30 days?

1.6%

EPSS score, percentile 75.4 of all scored records

How severe?

7.8 High

CVSS v3.1 base score, given by the CNA

What should I do?

CISA deadline 16 May 2022. Apply updates per vendor instructions.

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

Which versions are affected?

Affected

• from 10.0.0 to before 10.0.17763.2237
• from 10.0.0 to before 10.0.17763.2237
• from 10.0.0 to before 10.0.17763.2237
• from 10.0.0 to before 10.0.18363.1854
• from 10.0.0 to before 10.0.19043.1288
• from 10.0.0 to before 10.0.20348.288

and 5 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: 16 May 2022.

Advisories and patches

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

Linked from CISA's catalog entry

• https://nvd.nist.gov/vuln/detail/CVE-2021-40450

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 Win32k contains an unspecified vulnerability that allows for privilege escalation.

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

• CISA added CVE-2021-40450 to its Known Exploited Vulnerabilities (KEV) catalog on 25 Apr 2022.
• CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
• The due date CISA sets for the required action is 16 May 2022.
• The CVE record was published on 13 Oct 2021, 194 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 1.6% (percentile 75.4), 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

Win32k Elevation of Privilege Vulnerability

Win32k 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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