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CVE-2026-45498, known as UnDefend, is a denial-of-service vulnerability in the Microsoft Defender Antimalware Platform caused by uncontrolled resource consumption. A local attacker can abuse the flaw to prevent Defender definition updates, disrupting the availability and currency of antimalware protection.
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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.
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Patch, then assume compromise.
No valid public exploits. Mallory filtered out 4 candidates as fakes, detection scripts, or README-only repos.
All candidate exploits were filtered out by Mallory's validation.
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.
115 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A patched Microsoft Defender denial-of-service vulnerability that blocked definition updates through uncontrolled resource consumption; discussed as a distinct predecessor to BigDiskBuster.
A denial-of-service vulnerability caused by resource consumption in the Microsoft Defender Antimalware Platform. It is described as actively exploited and included in CISA's KEV catalog.
Previously disclosed Windows vulnerability referenced only in passing among earlier exploit publications.
A named Windows zero-day disclosed by Chaotic Eclipse; no further technical detail is provided in the content.
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.