An anonymous security researcher known as Nightmare Eclipse has released a new Microsoft Defender zero-day exploit called ShieldCrash shortly after Microsoft rolled out its September 2026 Patch Tuesday security updates.
ShieldCrash is described as a bypass for ShieldBreak, a Defender privilege escalation flaw that Microsoft patched recently. ShieldBreak itself was a bypass for another Defender vulnerability known as RoguePlanet, which was disclosed in June and patched by Microsoft in July.
According to Nightmare Eclipse, the ShieldCrash proof-of-concept can allow attackers to gain SYSTEM privileges on fully patched Windows 10, Windows 11 and Windows Server systems. However, the current proof-of-concept does not provide attackers with write access to the compromised systems.
The researcher claims Microsoft did not completely fix the underlying issue behind ShieldBreak. Under certain conditions, the same problem can still be triggered despite Microsoft’s security updates. Nightmare Eclipse said Microsoft made several changes to prevent the original exploit from being reused but missed another location where the vulnerability could still be exploited.
The released proof-of-concept demonstrates arbitrary file reading with SYSTEM privileges on supported Windows versions using the September 2026 updates. Nightmare Eclipse said the current release is only a basic proof of concept and suggested it could potentially be developed into a more complete SYSTEM exploit later.
The release is part of an ongoing dispute between Nightmare Eclipse and Microsoft over the company’s bug bounty and vulnerability disclosure practices. Microsoft has previously warned that it could take legal action against people involved in malicious activity that causes real harm to its customers.
Since April, the anonymous researcher has disclosed a series of zero-day vulnerabilities affecting Microsoft Defender, BitLocker and other Windows components. These include ShieldBreak, LegacyHive, RoguePlanet, BlueHammer, RedSun, YellowKey, GreenPlasma, MiniPlasma and UnDefend.
If this article helped you, please consider supporting our work. Every small contribution keeps Abijita.com independent and running.
Microsoft has already fixed the ShieldBreak, RoguePlanet, YellowKey, GreenPlasma and MiniPlasma vulnerabilities. However, according to the supplied report, several of the other flaws disclosed by Nightmare Eclipse still do not have an official Microsoft patch.
