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CVE-2026-55011 is a remote code execution vulnerability in Microsoft Defender caused by an integer underflow, also described as an integer wraparound condition. The flaw allows improper handling of numeric values such that a subtraction or related arithmetic operation can produce an unexpectedly small or wrapped value, which can then influence subsequent memory sizing, bounds checking, or processing logic. Microsoft classifies the issue as allowing an unauthorized attacker to execute code locally. Publicly available detail is limited, and the specific vulnerable component or function within Microsoft Defender has not been identified in the available information.
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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.
3 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A critical remote code execution vulnerability in Microsoft Defender.
A critical remote code execution vulnerability in Microsoft Defender.
A remote code execution vulnerability in Microsoft Defender.
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.