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CVE-2026-45498, known as UnDefend, is a local denial-of-service vulnerability in the Microsoft Defender Antimalware Platform and Microsoft Malware Protection Engine. An unauthenticated local attacker can cause Microsoft Defender to become unavailable. Affected versions include Microsoft Defender Antimalware Platform 4.18.26030.3011 and earlier and Microsoft Malware Protection Engine 1.1.26030.3008 and earlier. The underlying weakness type is not specified.
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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.
113 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
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.
A Windows Defender-related flaw/tool referenced as part of NightmareEclipse’s prior toolkit, described as blinding Defender and falsifying health status to the management console.
Another Microsoft-related zero-day mentioned only in passing in a list of disclosed bugs; no technical details are provided in this article.
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.