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Microsoft Defender update-blocking zero-day security flaw

Vulnerability
First reported
Last updated
Happening score
H score 7
1 unique sources, 1 articles

Summary

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A Microsoft Defender zero-day named BigDiskBuster can block platform/signature updates on supported Windows versions, freezing antivirus updates while it runs in the background. The flaw is being circulated as a public proof of concept rather than a fixed issue, leaving affected systems stuck on their current definitions and platform version. The disclosure also frames it as part of an earlier Defender flaw pattern, increasing the risk that similar update-blocking weaknesses can be reused.

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Timeline

  1. 22.09.2026 12:55 2 articles · 1h ago

    Microsoft Defender update-blocking zero-day security flaw

    Initial Disclosure

    A new BigDiskBuster proof of concept surfaced for Microsoft Defender, showing a way to block platform/signature updates on supported Windows builds. The background-running tool can leave the antivirus frozen at its current version.

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