A newly disclosed zero-day exploit, known as LegacyHive, affects fully patched Windows systems by targeting a flaw in the Windows User Profile Service. This local privilege escalation vulnerability, discovered by security researcher Chaotic Eclipse, allows attackers to gain elevated privileges on both desktop and server systems, despite the absence of any known CVE or security advisory from Microsoft. The LegacyHive proof-of-concept was released just hours after Microsoft's July 2026 Patch Tuesday, highlighting the ongoing risk of zero-day attacks1. The exploit's impact is significant, as it can be used to compromise even fully patched systems, emphasizing the need for immediate exposure assessment. This vulnerability matters to practitioners because it underscores the limited window of time available to patch newly disclosed vulnerabilities, making it essential to assess their exposure promptly to prevent potential attacks.