CVE-2026-21513 Microsoft Windows: security feature bypass
In plain words: A built-in safety check — like a warning before opening a downloaded file — can be skipped. Makes other attacks, like malicious downloads, work without the usual warning.
Confirmed exploited by CISA on · US federal patch deadline Mar 3, 2026
What to do
- Install Microsoft's security update for Windows. If no update exists, follow the vendor's workaround or stop using the product until one ships.
- Let the browser auto-update and relaunch it when it asks — the fix is not active until you do.
- Keep extensions to a minimum and remove ones you do not recognise.
- Stop using Internet Explorer and any browser that no longer gets updates.
Who is affected
Could reach you. This one is aimed at devices or apps of the kind people own.
What's at risk: A malicious or hacked website can be enough. Browser bugs are often the first step in a longer attack on the whole computer or phone.
The details
- Official name
- Microsoft MSHTML Framework Protection Mechanism Failure Vulnerability
- Product
- Microsoft Windows
- CISA description
- Microsoft MSHTML Framework contains a protection mechanism failure vulnerability that could allow an unauthorized attacker to bypass a security feature over a network.
- Type of flaw
- Security feature bypass (CWE-693)
- Confirmed exploited
- Feb 10, 2026
- US federal patch deadline
- Mar 3, 2026
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Answering about CVE-2026-21513 ·
Questions about CVE-2026-21513
Is CVE-2026-21513 being exploited?
Yes. CISA added CVE-2026-21513 to its Known Exploited Vulnerabilities catalog on Feb 10, 2026, which means there is reliable evidence of real-world attacks.
How do I fix CVE-2026-21513?
Install Microsoft's security update for Windows. If no update exists, follow the vendor's workaround or stop using the product until one ships. Let the browser auto-update and relaunch it when it asks — the fix is not active until you do.
Am I affected by CVE-2026-21513?
Only if you use Microsoft Windows. This one is aimed at devices or apps of the kind people own.