Nightmare Eclipse: Microsoft DCU threat, GreenPlasma/MiniPlasma unpatched, July 14 deadline

UPDATE (originally covered 2026-W21): Microsoft's Digital Crimes Unit issued a formal public statement on 28–29 May 2026 calling uncoordinated zero-day releases "never justifiable" and warning its DCU would "continue bringing cases against these actors and those that enable their criminal activity" (The Record, 2026-05-29). The pseudonymous researcher Nightmare Eclipse / Chaotic Eclipse responded by threatening a new vulnerability release on 14 July 2026 (the next Patch Tuesday).

Of the six Windows vulnerabilities the researcher has released since early April: BlueHammer (CVE-2026-33825), UnDefend (CVE-2026-45498), and RedSun (CVE-2026-41091) are patched and saw confirmed in-the-wild exploitation following PoC publication. YellowKey (CVE-2026-45585 — BitLocker bypass via Windows Recovery Environment, requiring physical access), GreenPlasma (LPE class), and MiniPlasma remain unpatched as of 30 May 2026. MiniPlasma specifically abuses the Windows Cloud Files Mini Filter Driver (cldflt.sys) to achieve a SYSTEM shell from a standard user session on fully-patched Windows 11; the root cause is assessed as an incomplete remediation of CVE-2020-17103 (no CVE yet assigned to MiniPlasma itself).

The July 14 release deadline should be treated as a hard date for resolving any outstanding Windows LPE chain gaps. Defenders on Windows 11 estates should monitor for cldflt.sys-related anomalies and consider AppLocker/WDAC policies blocking unsigned executables from low-privileged user sessions while patches are pending. Next Patch Tuesday: 10 June 2026.

UPDATE (originally covered 2026-05-15): Microsoft formally assigned CVE-2026-45585 to the BitLocker / WinRE bypass disclosed by "Nightmare Eclipse" on 2026-05-12 and confirmed there is still no security update. The MSRC update guide entry, published 2026-05-19, classifies it as CWE-77 (command injection in BitLocker / Windows Recovery Environment), CVSS 6.8 (AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H), with exploit-code maturity rated E:P (proof-of-concept) and remediation level RL:W (workaround only).

Microsoft's interim mitigation requires per-endpoint work on every device using TPM-only BitLocker (no PIN / password protector): mount the WinRE image, remove the autofstx.exe entry from the BootExecute registry value inside the WinRE image, commit the image, then re-establish BitLocker trust for WinRE. The MSRC FAQ states: "A successful attacker could bypass the BitLocker Device Encryption feature on the system storage device. An attacker with physical access to the target could exploit this vulnerability to gain access to encrypted data."

Practically: for fleets at scale (Swiss federal admin, cantonal endpoints, classified Windows devices), the more durable hardening is to add a BitLocker PIN or password protector rather than relying solely on TPM-only. The WinRE registry edit is fragile and breaks on Windows feature updates that re-stage the WinRE image; the PIN/password protector closes the exposure regardless of WinRE state.

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).

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.

Researcher "Nightmare Eclipse" published two new unpatched Windows zero-days on 2026-05-12–13 as full-disclosure drops after a disclosure dispute with Microsoft, bringing the total of unpatched Nightmare Eclipse Windows zero-days to four (BleepingComputer, 2026-05-13 · The Register, 2026-05-13 · NCSC-CH Security Hub #12574, 2026-05-14). YellowKey exploits a Windows Recovery Environment (WinRE) bug in NTFS transaction-log (TxF/FsTx) replay: crafted FsTx folder contents placed on a USB drive or the EFI partition are replayed by WinRE during startup, deleting winpeshl.ini — the file that suppresses the recovery shell — and dropping the attacker into a CMD prompt with the BitLocker-protected volume already mounted and readable. The current public PoC defeats TPM-only BitLocker configurations on Windows 11 and Windows Server 2022/2025; the researcher asserts the full bypass also defeats TPM+PIN but the unpublished variant is unconfirmed. MITRE ATT&CK: T1542.001 (Pre-OS Boot: System Firmware), T1006 (Direct Volume Access). GreenPlasma is a local privilege-escalation flaw in the CTFMON (Collaborative Translation Framework) service: an unprivileged user creates arbitrary section objects in SYSTEM-writable directories, which can be leveraged to manipulate privileged services for a SYSTEM token; the public PoC is partial and the exploit chain triggers a UAC prompt in default configurations. MITRE ATT&CK: T1134 (Access Token Manipulation), T1068 (Exploitation for Privilege Escalation). Neither vulnerability has been assigned a CVE nor received a Microsoft patch as of 2026-05-15; Microsoft states it is "actively investigating." A previous drop by the same researcher (BlueHammer, CVE-2026-33825, now patched) was confirmed used in real-world intrusions by Huntress in April 2026, demonstrating that this researcher's PoCs are operationally adopted. Immediate mitigations: require BitLocker pre-boot PIN (Group Policy Computer Configuration > Administrative Templates > Windows Components > BitLocker Drive Encryption > Require additional authentication at startup); set BIOS/UEFI boot password and disable USB/external-media boot; disable WinRE where operationally viable (reagentc /disable).