CVE-2026-21510: Microsoft Windows Shell Protection Mechanism Failure Vulnerability

Is it exploited?

Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 10 Feb 2026, the same day the CVE record was published.

How likely is exploitation in the next 30 days?

61.2%

EPSS score, percentile 99.2 of all scored records

How severe?

8.8 High

CVSS v3.1 base score, given by the CNA

What should I do?

Required action (CISA), due 3 Mar 2026: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Advisories and patches (1)

Which versions are affected?

Affected: 10.0.14393.0 up to, not including, 10.0.14393.8868; 10.0.17763.0 up to, not including, 10.0.17763.8389; 10.0.19044.0 up to, not including, 10.0.19044.6937; 10.0.19045.0 up to, not including, 10.0.19045.6937; 10.0.22631.0 up to, not including, 10.0.22631.6649; 10.0.22631.0 up to, not including, 10.0.22631.6649; 10.0.26100.0 up to, not including, 10.0.26100.7840; 10.0.26200.0 up to, not including, 10.0.26200.7840; 10.0.28000.0 up to, not including, 10.0.28000.1575; 10.0.28000.0 up to, not including, 10.0.28000.1575; 6.2.9200.0 up to, not including, 6.2.9200.25923; 6.2.9200.0 up to, not including, 6.2.9200.25923; 6.3.9600.0 up to, not including, 6.3.9600.23022; 6.3.9600.0 up to, not including, 6.3.9600.23022; 10.0.14393.0 up to, not including, 10.0.14393.8868; 10.0.14393.0 up to, not including, 10.0.14393.8868; 10.0.17763.0 up to, not including, 10.0.17763.8389; 10.0.17763.0 up to, not including, 10.0.17763.8389; 10.0.20348.0 up to, not including, 10.0.20348.4773; 10.0.25398.0 up to, not including, 10.0.25398.2149

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: 3 March 2026.

Advisories and patches

• Windows Shell Security Feature Bypass Vulnerability (Vendor advisory, Patch)

Linked from CISA's catalog entry

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21510
• https://nvd.nist.gov/vuln/detail/CVE-2026-21510

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 Shell contains a protection mechanism failure vulnerability that could allow an unauthorized attacker to bypass a security feature over a network.

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

• CISA added CVE-2026-21510 to its Known Exploited Vulnerabilities (KEV) catalog on 10 Feb 2026.
• 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 3 Mar 2026.
• The CVE record was published on 10 Feb 2026, the same day it was added to KEV.
• The CVE record carries a CVSS v3.1 base score of 8.8 (High), given by its CNA.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 61.2% (percentile 99.2), 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 Shell Security Feature Bypass Vulnerability

Protection mechanism failure in Windows Shell allows an unauthorized attacker to bypass a security feature over a network.

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

Weakness

• CWE-693: Protection Mechanism Failure

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

Timeline

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