A security researcher using the “Nightmare Eclipse” handle has released a Windows zero-day exploit dubbed LegacyHive that allows attackers to escalate privileges on up-to-date Windows systems.

Nightmare Eclipse published a proof-of-concept (PoC) exploit hours after Microsoft released its July 2026 Patch Tuesday updates, saying that it abuses a security vulnerability in the Windows User Profile Service, which has yet to receive a CVE ID for easier tracking.

However, unlike previous exploits released by NightmwareEclipse, the LegacyHive PoC has been modified to require additional credentials, making it harder for attackers to weaponize the vulnerability.