How severe is CVE-2026-21513?

CVE-2026-21513 has a CVSS 3.1 base score of 8.8 (HIGH). EPSS estimates a 15.9% probability of exploitation in the next 30 days. It is listed in the CISA Known Exploited Vulnerabilities catalog.

CVE-2026-21513: MSHTML Framework Security Feature Bypass Vulnerability

CISA Known Exploited Vulnerabilities

Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability is confirmed as actively exploited and is listed in the CISA KEV catalog.

Added to KEV

2026-02-10

Remediation due

2026-03-03

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.

CISA notes
https://msrc.microsoft.com/update-guide/advisory/CVE-2026-21513 ; https://nvd.nist.gov/vuln/detail/CVE-2026-21513

Description

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

Severity

CVSS 3.1 · CNA8.8 HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

SSVC · CISA-ADP

Exploitationactive

Automatableno

Technical impacttotal

Exploitation Context

as of October 17, 2026

All KEV statistics→

CISA added CVE-2026-21513 to the KEV catalog on the day its CVE record was published. The median for entries added in 2026 so far is 14 days.
It is one of 391 Microsoft entries in the CISA KEV catalog, and one of 40 added in 2026.
Its current EPSS score (15.9%) is higher than that of 32% of CISA KEV entries.

Affected Products

Vendor	Product	Affected versions
Microsoft	Microsoft Windows 10 Version 1607	10.0.14393.0 to <10.0.14393.8868
Microsoft	Microsoft Windows 10 Version 1809	10.0.17763.0 to <10.0.17763.8389
Microsoft	Microsoft Windows 10 Version 21H2	10.0.19044.0 to <10.0.19044.6937
Microsoft	Microsoft Windows 10 Version 22H2	10.0.19045.0 to <10.0.19045.6937
Microsoft	Microsoft Windows 11 version 22H3	10.0.22631.0 to <10.0.22631.6649
Microsoft	Microsoft Windows 11 Version 23H2	10.0.22631.0 to <10.0.22631.6649
Microsoft	Microsoft Windows 11 Version 24H2	10.0.26100.0 to <10.0.26100.7840
Microsoft	Microsoft Windows 11 Version 25H2	10.0.26200.0 to <10.0.26200.7840
Microsoft	Microsoft Windows 11 version 26H1	10.0.28000.0 to <10.0.28000.1575
Microsoft	Microsoft Windows 11 Version 26H1	10.0.28000.0 to <10.0.28000.1575
Microsoft	Microsoft Windows Server 2012	6.2.9200.0 to <6.2.9200.25923
Microsoft	Microsoft Windows Server 2012 (Server Core installation)	6.2.9200.0 to <6.2.9200.25923
Microsoft	Microsoft Windows Server 2012 R2	6.3.9600.0 to <6.3.9600.23022
Microsoft	Microsoft Windows Server 2012 R2 (Server Core installation)	6.3.9600.0 to <6.3.9600.23022
Microsoft	Microsoft Windows Server 2016	10.0.14393.0 to <10.0.14393.8868
Microsoft	Microsoft Windows Server 2016 (Server Core installation)	10.0.14393.0 to <10.0.14393.8868
Microsoft	Microsoft Windows Server 2019	10.0.17763.0 to <10.0.17763.8389
Microsoft	Microsoft Windows Server 2019 (Server Core installation)	10.0.17763.0 to <10.0.17763.8389
Microsoft	Microsoft Windows Server 2022	10.0.20348.0 to <10.0.20348.4773
Microsoft	Microsoft Windows Server 2022, 23H2 Edition (Server Core installation)	10.0.25398.0 to <10.0.25398.2149
Microsoft	Microsoft Windows Server 2025	10.0.26100.0 to <10.0.26100.32370
Microsoft	Microsoft Windows Server 2025 (Server Core installation)	10.0.26100.0 to <10.0.26100.32370

References

3 Links

Vendor advisories

MSHTML Framework Security Feature Bypass Vulnerability

Other references

Record Details

Published

2026-02-10

Last updated

2026-08-19

Assigner (CNA)

microsoft

Credited to

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Tool categories

Application Security Tools

CVE record data © The MITRE Corporation, used under the CVE Terms of Use. Exploited-in-the-wild data from the CISA Known Exploited Vulnerabilities catalog (CC0). Exploit prediction scores by FIRST EPSS (first.org/epss). This site is not endorsed or certified by MITRE, NVD, CISA, or FIRST.

CVE-2026-21513