Right on the heels of Microsoft releasing a record number of security patches, a researcher has published exploit code that can enable low-privilege Windows accounts to make sensitive changes to administrator accounts.

The exploit, which multiple researchers say works, is sending Microsoft scrambling, yet again, to patch a zero-day released by an anonymous researcher who has complained about the software maker’s handling of their bug reports. To date, the pseudonymous NightmareEclypse has published nine such exploits, including Tuesday’s HiveLegacy.

HiveLegacy is an elevation-of-privilege exploit that targets a vulnerability residing in the Windows User Profile Service. It allows users (and with more work likely processes) with limited system rights to compromise an admin user’s account by modifying its classes registry hive, a resource that ensures the correct application opens when certain types of files are clicked on in Windows Explorer.

At a minimum, that means the attacker can modify the Windows registry associated with an administrator account. As written, the exploit requires the attacker to know another user’s credentials. The account need not be admin. An attacker must also know the username of a third account, also with or without admin status, on the machine.

Much ado about nothing? Not according to NightmareEclypse, who said the proof-of-concept code included in the report was stripped down to prevent attackers from using it maliciously. But for Microsoft, it’s business as usual: scrambling to patch their latest vulnerability while hoping users keep their guard up.