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CVE-2026-21513: Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability

criticalknown exploitedCVE-2026-21513
Actively exploited. At least one CVE in this advisory is listed in the CISA Known Exploited Vulnerabilities catalog — exploitation has been observed in the wild. Treat remediation as urgent.
Microsoft MSHTML Framework contains a protection mechanism failure vulnerability that could allow an unauthorized attacker to bypass a security feature over a network.

CSIRTS triage

vendor: Microsoftproduct: MSHTML FrameworkAuthentication bypass
What
A protection mechanism failure vulnerability could allow an unauthorized attacker to bypass a security feature over a network.
Who is affected
Deployments of Microsoft MSHTML Framework.
Urgency
Remediation is urgent due to active exploitation and critical severity.
Action
Apply the latest security patch provided by Microsoft.

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Details

Source
CISA Known Exploited Vulnerabilities (US · database · site)
Severity
critical
Published
2026-02-10
Exploitation
Observed in the wild (CISA KEV)

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-21513

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2026-21513coverage & exploitation statusNVD · CVE.org

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