MiniPlasma zero-day gives SYSTEM access on fully patched Windows 11

A researcher known as Chaotic Eclipse has released a working Windows privilege escalation exploit that grants SYSTEM access on fully patched Windows 11 machines, including those running the latest May 2026 Patch Tuesday update.

The exploit, named MiniPlasma, was published recently alongside both source code and a compiled executable on GitHub. BleepingComputer confirmed it works on a standard user account, opening a SYSTEM-level command prompt on a fresh Windows 11 Pro installation. Security researcher Will Dormann of Tharros independently verified the results.

A bug that was supposed to be fixed in 2020

The flaw sits in the Windows Cloud Filter driver, cldflt.sys, specifically in a routine called HsmOsBlockPlaceholderAccess. The bug is not new. Google Project Zero researcher James Forshaw reported the same issue to Microsoft in September 2020, and it was assigned CVE-2020-17103 and supposedly patched in December of that year. Chaotic Eclipse ran Forshaw's original proof-of-concept unmodified and reports it worked as is. "I'm unsure if Microsoft just never patched the issue or the patch was silently rolled back at some point for unknown reasons," the researcher wrote on the disclosure.

The exploit abuses how the Cloud Filter driver handles registry key creation through an undocumented API, allowing a standard user to create arbitrary registry keys in the .DEFAULT user hive without the access checks that should stop them. It involves a race condition, so the success rate varies, but BleepingComputer's confirmed results suggest it is reliable enough on real hardware. One exception: it does not work on the latest Windows 11 Insider Preview Canary build.

Part of a deliberate campaign

MiniPlasma is yet another Windows zero-day disclosure from Chaotic Eclipse in the past six weeks. The researcher started in April with BlueHammer, a Windows Defender local privilege escalation vulnerability that Microsoft patched on April 14 Patch Tuesday as CVE-2026-33825, just days after it was publicly disclosed on April 3. That was followed by RedSun, a second LPE in Defender that Microsoft reportedly fixed silently without assigning a CVE. UnDefend, a Defender denial-of-service tool that blocks security definition updates, came next. Then YellowKey, a BitLocker bypass that unlocks encrypted drives via the WinRE recovery environment. Then GreenPlasma, a CTFMON framework privilege escalation for which the researcher withheld part of the exploit code. Now MiniPlasma.

All three original exploits, BlueHammer, RedSun, and UnDefend, were confirmed being exploited in real attacks by Huntress researchers shortly after public disclosure. The researcher is explicit about why these are being released: dissatisfaction with how Microsoft handles bug bounty reports and patch verification. Microsoft has not commented on MiniPlasma specifically. The company previously told BleepingComputer that it "supports coordinated vulnerability disclosure" as a widely adopted industry practice.