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

Exp

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

Published: 2026-02-10 Last update: 2026-03-30 Assigner: [email protected] Source: [email protected]

NVD Status：Analyzed，CVE State: published

View at NVD, CVE.org, EUVD

Threat Intelligence & Risk Assessment for CVE-2026-21513

KEV EPSS CVSS CWE Affected

Conclusion & alert: CVE-2026-21513 is rated Critical Active Threat (97/100): CVSS High severity, with high exploitation likelihood (EPSS 27.98%, 97th percentile). Core evidence: CISA KEV confirms active exploitation (added 2026-02-10) affecting Microsoft / Windows. a weakness (CWE-693) Unauthenticated remote administrative access may be possible. EPSS rose +3.02% over the last day, indicating growing attacker interest. Mandatory action: The CISA remediation deadline has passed—treat as an emergency patch priority.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

CISA KEV Record for CVE-2026-21513

Name: Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability · CISA KEV detail

Exploit added: 2026-02-10

Action 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.

Exploit prediction scoring system (EPSS) score for CVE-2026-21513

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-03	24.96%	27.98%	+3.02%
2	2026-05-29	22.11%	24.96%	+2.85%
3	2026-05-28	—	22.11%	—

Full EPSS history (28 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-21513

CVSS metrics for this CVE.

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
8.8	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	5.9	[email protected]

Weakness enumeration for CVE-2026-21513

CWE-693 MITRE ↗

Affected software / configurations for CVE-2026-21513

Vendor	Product	Version	Raw CPE
microsoft	windows_10_1607	< 10.0.14393.8868	cpe:2.3:o:microsoft:windows_10_1607:::::::x64:*
microsoft	windows_10_1607	< 10.0.14393.8868	cpe:2.3:o:microsoft:windows_10_1607:::::::x86:*
microsoft	windows_10_1809	< 10.0.17763.8389	cpe:2.3:o:microsoft:windows_10_1809:::::::x64:*
microsoft	windows_10_1809	< 10.0.17763.8389	cpe:2.3:o:microsoft:windows_10_1809:::::::x86:*
microsoft	windows_10_21h2	< 10.0.19044.6937	cpe:2.3:o:microsoft:windows_10_21h2:::::::arm64:*
microsoft	windows_10_21h2	< 10.0.19044.6937	cpe:2.3:o:microsoft:windows_10_21h2:::::::x64:*
microsoft	windows_10_21h2	< 10.0.19044.6937	cpe:2.3:o:microsoft:windows_10_21h2:::::::x86:*
microsoft	windows_10_22h2	< 10.0.19045.6937	cpe:2.3:o:microsoft:windows_10_22h2:::::::arm64:*
microsoft	windows_10_22h2	< 10.0.19045.6937	cpe:2.3:o:microsoft:windows_10_22h2:::::::x64:*
microsoft	windows_10_22h2	< 10.0.19045.6937	cpe:2.3:o:microsoft:windows_10_22h2:::::::x86:*
microsoft	windows_11_23h2	< 10.0.22631.6649	cpe:2.3:o:microsoft:windows_11_23h2:::::::arm64:*
microsoft	windows_11_23h2	< 10.0.22631.6649	cpe:2.3:o:microsoft:windows_11_23h2:::::::x64:*
microsoft	windows_11_24h2	< 10.0.26100.7781	cpe:2.3:o:microsoft:windows_11_24h2:::::::arm64:*
microsoft	windows_11_24h2	< 10.0.26100.7781	cpe:2.3:o:microsoft:windows_11_24h2:::::::x64:*
microsoft	windows_11_25h2	< 10.0.26200.7781	cpe:2.3:o:microsoft:windows_11_25h2:::::::arm64:*
microsoft	windows_11_25h2	< 10.0.26200.7781	cpe:2.3:o:microsoft:windows_11_25h2:::::::x64:*
microsoft	windows_server_2012	—	cpe:2.3:o:microsoft:windows_server_2012:-:::::::*
microsoft	windows_server_2012	r2	cpe:2.3:o:microsoft:windows_server_2012:r2:::::::*
microsoft	windows_server_2016	< 10.0.14393.8868	cpe:2.3:o:microsoft:windows_server_2016:::::-::x64:
microsoft	windows_server_2019	< 10.0.17763.8389	cpe:2.3:o:microsoft:windows_server_2019:::::-::x64:
microsoft	windows_server_2022	< 10.0.20348.4711	cpe:2.3:o:microsoft:windows_server_2022:::::-::x64:
microsoft	windows_server_2022_23h2	< 10.0.25398.2149	cpe:2.3:o:microsoft:windows_server_2022_23h2:::::-::x64:
microsoft	windows_server_2025	< 10.0.26100.32313	cpe:2.3:o:microsoft:windows_server_2025:::::::x64:*

References for CVE-2026-21513

URL	Tags
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21513	Vendor Advisory
https://www.vicarius.io/vsociety/posts/cve-2026-21513-detection-script-security-feature-bypass-vulnerability-in-mshtml-framework	Third Party Advisory
https://www.vicarius.io/vsociety/posts/cve-2026-21513-mitigation-script-security-feature-bypass-vulnerability-in-mshtml-framework	Mitigation Third Party Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21513	US Government Resource

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