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Microsoft Defender scans break after ShieldBreak zero

Feeds.4Sysops •IT News • August 19, 2026

Microsoft Defender is reportedly failing quick, full, and offline scans after updates intended to address the ShieldBreak zero-day, which had bypassed Microsoft’s RoguePlanet fix and enabled local users to gain SYSTEM privileges. The regression appears to affect the antimalware engine itself, leaving administrators with incomplete protection while Microsoft prepares a replacement update. Source

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This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.

Windows Defender Crashes Following Security Update Fix for ShieldBreak Vulnerability Microsoft has addressed a bug causing Windows Defender to crash during scans after a recent security update aimed at fixing the ShieldBreak zero-day vulnerability. Users reported access violation errors and service stoppages, leading to incomplete scans and potential vulnerabilities in their systems. The issue affected both Windows 10 and Windows 11, prompting some users to reinstall their operating systems. Microsoft confirmed the bug and released a signature update (version 1.457.236.0) to resolve the issue. Users are advised to update their systems via Windows Update to ensure they have the latest security intelligence. The problem was first reported on August 16, 2026, and has since been acknowledged by Microsoft. The crash issue was linked to the attempts to mitigate the ShieldBreak vulnerability, which allowed local users to gain SYSTEM privileges. 10 sources 58

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Microsoft Defender scans break after ShieldBreak zero

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Extracted Entities

Attack Types (1)

MITRE ATT&CK (1)

Vulnerabilities (1)