Disgruntled researcher leaks Defender zero-days, leaving Windows users exposed
TL;DR Summary
A disgruntled security researcher leaked three Microsoft Defender zero-days—BlueHammer, RedSun and UnDefend—exposing over a billion Windows users; BlueHammer has been patched in the April 2026 updates, while RedSun and UnDefend remain unpatched but are already being exploited in the wild. Users should install the April 2026 security updates now and monitor for future patches, with additional antivirus protection to bolster defenses.
- Over 1 billion Windows users at risk after disgruntled security researcher leaks Defender zero-days Tom's Guide
- Three Microsoft Defender Zero-Days Actively Exploited; Two Still Unpatched The Hacker News
- Hackers are abusing unpatched Windows security flaws to hack into organizations TechCrunch
- Recently leaked Windows zero-days now exploited in attacks BleepingComputer
- RedSun: Windows 0day when Defender becomes the attacker CloudSEK
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