Nightmare Eclipse

BigDiskBuster Exploit Blocks Microsoft Defender Updates on All Supported Windows Versions

Security researcher Abdelhamid Naseri, known as Nightmare Eclipse, has released BigDiskBuster, a new exploit targeting Microsoft Defender that prevents the platform and antivirus signatures from receiving updates. The tool leaves Windows systems protected only by an outdated threat database while the interface continues to display normal status indicators. BigDiskBuster works across all currently supported Windows versions but requires continuous background execution. The researcher has published the source code on GitHub and acknowledged that the current implementation contains bugs requiring further refinement. The technique closely resembles the earlier UnDefend tool released in April, which similarly interfered with Defender update mechanisms. Naseri has disclosed nearly a dozen proof-of-concept exploits since April affecting Microsoft Defender, BitLocker, and other Windows components, including ShieldCrash, ShieldBreak, RoguePlanet, LegacyHive, BlueHammer, RedSun, YellowKey, and Plasma variants. Microsoft has not yet issued a patch for BigDiskBuster and previously criticized uncoordinated public disclosures of working exploits.

Microsoft Defender Zero-Day ShieldBreak Enables SYSTEM Privilege Escalation, Bypassing July Rogue Planet Patch

Security researcher Nightmare Eclipse has publicly disclosed a new zero-day vulnerability named ShieldBreak in Microsoft Defender that allows any standard Windows account to escalate privileges directly to SYSTEM level. The flaw exploits a TOCTOU race condition in Defender's file scanning API callbacks, enabling attackers to swap file contents during the brief window when the scanner reads the file. Although linked to the earlier Rogue Planet vulnerability (CVE-2026-50656), the July patch did not fully address the attack surface, and an adjusted proof-of-concept continues to work on patched systems. Defender's high privileges and trusted status in enterprise environments amplify the risk, as compromised processes can execute malicious actions that appear legitimate in logs. Public disclosure without prior private reporting leaves a window of exposure until Microsoft issues an official fix. Blue teams are advised to enforce strict local permissions, monitor for anomalous Defender process behavior such as unusual child processes or repeated file handle operations, and implement layered defenses including application whitelisting and network segmentation.

Windows Lacks Official Patch for LegacyHive Zero-Day; 0Patch Delivers Free Micro-Patch

A zero-day vulnerability named LegacyHive has been discovered in the Windows user profile service, allowing any standard user to mount another user's registry hive with full access. The flaw was reported on July 14 by researcher Nightmare Eclipse, coinciding with Microsoft's Patch Tuesday, and enables extraction of stored secrets or persistence by modifying registry settings that execute code on the next administrator login. Microsoft has acknowledged the issue and is investigating, but no official fix has been released yet. ACROS Security stepped in with a free micro-patch through its 0Patch platform that neutralizes the exploit by redirecting it to a harmless temporary hive instead of the administrator profile. The protection is available for Windows 10 version 2004 and later, as well as Windows Server 2022 and newer releases, and requires only registration and agent installation without a reboot. Researchers Will Dormann and Kevin Beaumont have independently confirmed the exploit's functionality, with Beaumont also publishing Microsoft Defender for Endpoint queries to detect related attacks.

Windows Defender Patch for RoguePlanet Zero-Day Vulnerability May Exhaust Disk Space on Windows Systems

Microsoft released a security update addressing the RoguePlanet zero-day vulnerability (CVE-2026-50656) in the Microsoft Malware Protection Engine used by Windows Defender. The flaw, disclosed earlier by researcher NightmareEclipse, allowed remote attackers to gain administrative control over Windows 10 and Windows 11 even when real-time protection was disabled. While the patch was intended to resolve the issue and deploy automatically, the researcher now claims it introduces a new problem involving excessive disk writes. Specifically, the update may cause Defender to cache extremely large Zone.Identifier alternate data streams without size limits, potentially filling the entire drive. The attack vector involves a malicious SMB server that serves oversized metadata streams while maintaining the connection. Microsoft has not yet confirmed the reported behavior, and tensions between the company and the researcher continue over disclosure practices and bug bounty rewards.