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CVE-2026-21513 is a security feature bypass vulnerability in the Microsoft MSHTML Framework, the legacy Internet Explorer HTML rendering engine still used by Windows components to process HTML content. The flaw is described as a protection mechanism failure that allows a remote, unauthenticated attacker to bypass file execution and trust-related security prompts over a network. Reported exploitation scenarios involve delivering a crafted HTML file or weaponized Windows shortcut that causes Windows and MSHTML handling to treat content from an untrusted network source in a way that bypasses intended protections, including restrictions associated with untrusted-origin files and SmartScreen-style warning flows. Public reporting indicates the vulnerability has been exploited in the wild, including as part of exploit chains using malicious LNK files, and that successful exploitation may be chained to achieve remote code execution.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
175 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An MSHTML security bypass vulnerability identified as one of the CVEs being tested by the malware delivery infrastructure.
A specific vulnerability referenced only as smaller test material in the exposed lab; no technical details are provided in the content.
An MSHTML bypass vulnerability mentioned as a secondary file-handling flaw for which the operator kept smaller test sets.
An MSHTML Framework security feature bypass vulnerability caused by a protection-mechanism failure.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.