technology
Microsoft Defender update allows disk space fill
A patch released Wednesday for a zero-day flaw in the Microsoft Malware Protection Engine can cause Windows machines to write files large enough to exhaust available disk space. The researcher who disclosed the flaw said the new code creates a leak in mpengine.dll and bypasses normal file-size limits.
Jul 9, 4:52 PM·1m read2 sources
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A Microsoft update issued Wednesday to address a zero-day vulnerability in its Defender security engine may allow attackers to consume all available disk space on affected Windows machines. The patch targets RoguePlanet, tracked as CVE-2026-50656, which permits remote administrative access to Windows 10 and Windows 11 systems even when real-time protection is disabled.
The company said the fix is delivered automatically through the Microsoft Malware Protection Engine and requires no user action. Wednesday’s update also added defense-in-depth changes intended to strengthen security features.
dll when the driver attempts to open a file. Identifier ADS file regardless of its size. Defender normally enforces hard limits on file sizes during scanning and quarantining. The researcher wrote that the implementation makes sense because quarantining a very large file would exhaust disk space, yet the spynet functions create an exception that allows unlimited local caching.
The researcher disclosed the original vulnerability in June along with exploit code. Over the past several months the same individual has published multiple other zero-days that prompted Microsoft to issue patches.
