CVE-2021-40449: Microsoft Windows Win32k Privilege Escalation Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 17 Nov 2021, 35 days after the CVE record was published.

How likely is exploitation in the next 30 days?

81.9%

EPSS score, percentile 99.6 of all scored records

How severe?

7.8 High

CVSS v3.1 base score, given by the CNA

What should I do?

CISA deadline 1 Dec 2021. 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 10.0.19041.1288
• from 10.0.0 to before 10.0.20348.288

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: 1 December 2021.

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-2021-40449

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

Unspecified vulnerability allows for an authenticated user to escalate privileges.

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

• CISA added CVE-2021-40449 to its Known Exploited Vulnerabilities (KEV) catalog on 17 Nov 2021.
• CISA marks it as known to be used in ransomware campaigns.
• The due date CISA sets for the required action is 1 Dec 2021.
• The CVE record was published on 13 Oct 2021, 35 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 81.9% (percentile 99.6), 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.

Weakness

• CWE-416: Use After Free

CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.

Timeline

References

• portal.msrc.microsoft.com
• packetstormsecurity.com

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