New Windows Defender zero-day enables system privileges escalation

Wednesday 10 June 2026 - 11:17

By: Dakir Madiha

New Windows Defender zero-day enables system privileges escalation

A new security flaw has emerged in Microsoft Defender shortly after the release of a major Patch Tuesday update cycle. The vulnerability allows attackers to gain SYSTEM-level privileges on fully updated Windows 10 and Windows 11 machines. The issue stems from a race condition inside Microsoft Defender, exposing systems even after recent security patches were applied.

The exploit, named RoguePlanet, was released as a proof-of-concept by a security researcher known as Nightmare Eclipse. The code demonstrates how local privilege escalation can be achieved on systems that have installed the June 2026 cumulative update KB5094126. Independent security analysis confirmed that the exploit functions as described and can be reproduced under real-world conditions.

ThreatLocker, a cybersecurity company, validated the findings after testing the exploit on updated Windows 11 systems. Its engineers confirmed that the attack can successfully elevate privileges under specific conditions, although execution depends on timing due to the race condition. The company noted that application allowlisting can block the exploit by restricting unauthorized execution paths on affected systems.

The researcher behind RoguePlanet stated that the exploit originally targeted remote code execution through Microsoft Defender handling of SMB share files, but later changes to Microsoft’s API forced a shift toward local privilege escalation. The researcher also described variable success rates across machines, indicating inconsistent exploitation depending on system behavior.

This disclosure is part of a broader campaign that has seen multiple zero-day releases targeting Windows components in recent months. Microsoft’s latest Patch Tuesday addressed more than 200 vulnerabilities, including several previously disclosed flaws. Among them was a privilege escalation issue in Defender that was already known to be actively exploited in the wild, highlighting continued pressure on the company’s security response cycle.

Microsoft initially reacted strongly to the wave of disclosures, suggesting possible legal action against individuals causing harm. The company later reversed its position and returned to a coordinated vulnerability disclosure framework. Despite this shift, the researcher continued publishing additional exploits through independent infrastructure.