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CVE-2026-45498, also known as UnDefend, is a Microsoft Defender denial-of-service vulnerability. Successful exploitation can force a denial-of-service condition that disables Microsoft Defender entirely. The vulnerability was observed in the wild and was significant enough to be added to CISA’s Known Exploited Vulnerabilities catalog. Publicly available reporting in the available material does not provide sufficient technical detail about the precise root cause, vulnerable function, or code path to support a more specific description.
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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 valid public exploits. Mallory filtered out 3 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.
102 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Another Microsoft Defender vulnerability previously disclosed by the same researcher and mentioned only for background comparison.
A previously disclosed and patched Microsoft Defender vulnerability mentioned only as background context.
A previously disclosed Microsoft vulnerability referenced as one of several zero-days published by the same researcher; no further technical details are provided in the content.
A Microsoft Defender vulnerability previously disclosed by Chaotic Eclipse and since patched by Microsoft.
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.