Windows Cloud Filter driver cldflt.sys privilege escalation (MiniPlasma PoC)

Chaotic Eclipse / Nightmare Eclipse — MiniPlasma confirmed SYSTEM on a fully-patched Windows 11; sixth zero-day in six weeks

The Windows zero-day cluster carried a material technical update beyond the 2026-05-30 daily. MiniPlasma — the sixth zero-day the "Chaotic Eclipse" researcher has dropped in six weeks — is a local privilege escalation in the Windows Cloud Filter driver (cldflt.sys) that reuses CVE-2020-17103, the researcher claiming the 2020 patch was incomplete or partially reverted. ThreatLocker independently confirmed MiniPlasma achieves SYSTEM on a fully-patched Windows 11 running the May 2026 cumulative update — i.e. there is no configuration that closes it today. Three earlier drops in the series (BlueHammer, RedSun, UnDefend) have been observed in real attacks. Microsoft's DCU has called the uncoordinated releases "never justifiable" but has shipped no out-of-band fix; June 10 Patch Tuesday is the first fix opportunity (. Until then, treat any cldflt.sys-adjacent LPE as live.

Chaotic Eclipse Windows zero-days — MiniPlasma is third PoC in series; cldflt.sys CfAbortHydration path, claimed re-exploitable CVE-2020-17103 regression

UPDATE (originally covered 2026-05-15): Researcher "Chaotic Eclipse" / "Nightmare Eclipse" released a third unpatched Windows LPE PoC on 2026-05-17 — MiniPlasma — extending the YellowKey and GreenPlasma series covered in the 2026-05-15 daily (BleepingComputer, 2026-05-17; The Hacker News, 2026-05-18). The material new technical detail: MiniPlasma targets the cldflt.sys Cloud Filter Mini Filter Driver — specifically the HsmOsBlockPlaceholderAccess routine — and abuses the undocumented CfAbortHydration API to create arbitrary registry keys in the .DEFAULT user hive without proper ACL checks, escalating from standard user to SYSTEM. The flaw was originally reported by Google Project Zero (James Forshaw) in September 2020 and nominally patched in December 2020 as CVE-2020-17103; Chaotic Eclipse asserts the exact same code path remains exploitable on fully-patched Windows 11 with May 2026 cumulative updates applied. Will Dormann independently confirmed the PoC opens a SYSTEM cmd.exe reliably on Windows 11 Pro fully patched. The exploit reportedly fails on the latest Insider Preview Canary builds, suggesting Microsoft has a fix in the pipeline but has not yet released an out-of-band patch. ThreatLocker published two registry-path hunt pivots: \Registry\User\Software\Policies\Microsoft\CloudFiles\BlockedApps* and \Registry\User\.DEFAULT\Volatile Environment*.

Defender takeaway: the proliferation of unpatched LPEs from one researcher signals an extended period of SYSTEM-shell availability for any attacker that lands user-level execution on Windows endpoints. Sysmon EID 13 (RegistryEvent / SetValue) on the .DEFAULT hive from non-SYSTEM processes is the primary hunt pivot; Sysmon EID 6 driver-load monitoring catches related driver-abuse paths. Hardening: BitLocker PIN mitigates the companion YellowKey BitLocker bypass; disabling Cloud Files / OneDrive integration removes the MiniPlasma attack surface but is not practical in most environments. MITRE T1068 (Exploitation for Privilege Escalation).

Windows "Chaotic Eclipse" zero-day proliferation — YellowKey, GreenPlasma, MiniPlasma

The researcher cluster "Chaotic Eclipse" / "Nightmare Eclipse" continued releasing unpatched Windows LPE/bypass PoCs across the window. On 2026-05-19 a third PoC — MiniPlasma — landed, targeting the cldflt.sys CfAbortHydration path and claiming a re-exploitable regression of the 2020-era CVE-2020-17103. On 2026-05-20 Microsoft formally assigned CVE-2026-45585 to the BitLocker/WinRE bypass (YellowKey) disclosed on 2026-05-12 and published a WinRE mitigation — but confirmed there is still no security update for the cluster; the earliest fix window remains the June 2026 Patch Tuesday. Three public PoCs (YellowKey, GreenPlasma, MiniPlasma) now exist against the Windows-centric desktop estates standard in CH/EU federal and cantonal administrations. Until a patch ships, enforce BitLocker PIN/Network-Unlock GPOs and AppLocker/WDAC rules on ctfmon.exe injection paths, and segregate privileged accounts from the workstation tier.