A new vulnerability dubbed the Windows MiniPlasma zero-day exploit is allowing attackers to bypass security boundaries and gain full SYSTEM privileges on fully patched Windows machines. The discovery is particularly alarming because it appears to be a “zombie” bug—a flaw that was reported and purportedly fixed years ago, only to resurface in modern versions of the operating system.
The exploit was brought to light by a researcher operating under the pseudonym Chaotic Eclipse (also known as Nightmare Eclipse). Along with the announcement, the researcher released a proof-of-concept (PoC) including both the source code and a compiled executable on GitHub, providing a roadmap for how the elevation of privilege can be achieved.
At the heart of the issue is a failure in the patching process. Chaotic Eclipse claims that the vulnerability is identical to one originally reported to Microsoft in September 2020 by James Forshaw, a researcher with Google Project Zero. While Microsoft assigned the flaw the identifier CVE-2020-17103 and stated it was resolved in December 2020, the MiniPlasma exploit suggests the fix was either ineffective or inadvertently rolled back in subsequent updates.
The technical failure in the Cloud Filter driver
The vulnerability resides within the cldflt.sys Cloud Filter driver, specifically impacting the HsmOsBlockPlaceholderAccess routine. For those unfamiliar with the plumbing of Windows, this driver manages how the system handles “placeholder” files—files that exist in the cloud but appear locally on your drive.
The exploit leverages an undocumented API known as CfAbortHydration. By abusing how the driver handles registry key creation through this API, an attacker with standard user permissions can create arbitrary registry keys in the .DEFAULT user hive. Because these keys are created without proper access checks, they can be used to trick the system into granting the user the highest possible level of authority: SYSTEM privileges.
In practical terms, gaining SYSTEM access is the “holy grail” for an attacker. While a standard user is restricted from modifying core system files or accessing other users’ data, a SYSTEM-level account has total control over the local machine, allowing for the installation of persistent malware, the disabling of antivirus software, and the theft of sensitive credentials.
Independent verification has added weight to these claims. Will Dormann, a principal vulnerability analyst at Tharros, confirmed that the exploit functioned in his tests on the latest public release of Windows 11. Interestingly, Dormann noted that the flaw did not appear to work in the latest Windows 11 Insider Preview Canary build, suggesting that a genuine fix may finally be in the pipeline.
A pattern of protest and disclosure
MiniPlasma is not an isolated incident. It is the latest entry in a targeted campaign of disclosures by Chaotic Eclipse, who has spent recent weeks releasing a string of Windows vulnerabilities. This “disclosure spree” appears to be less about traditional security research and more about a personal and professional grievance against Microsoft.
The researcher’s recent releases include a variety of high-impact tools and exploits:
- BlueHammer: A local privilege escalation flaw tracked as CVE-2026-33825.
- RedSun: Another privilege escalation vulnerability, which the researcher claims Microsoft patched silently without assigning a CVE.
- UnDefend: A tool designed to cause a Denial of Service (DoS) within Windows Defender.
- YellowKey: A BitLocker bypass affecting Windows 11 and Windows Server 2022/2025, allowing access to unlocked drives protected by TPM-only configurations.
- GreenPlasma: A separate exploit released alongside YellowKey.
The motivation behind these releases is explicit. Chaotic Eclipse claims they are disclosing these zero-days in protest of Microsoft’s bug bounty and vulnerability-handling processes. In a series of statements, the researcher alleged a hostile relationship with the corporation, claiming that Microsoft representatives told them they would “ruin my life” and subsequently “mopped the floor” with them through “childish games.”
What In other words for Windows users
For the average user, the immediate risk is “local” privilege escalation. This means that for MiniPlasma to be dangerous, an attacker must already have a foothold on the machine—perhaps through a phishing email or a malicious download. Once inside as a low-privilege user, they can use MiniPlasma to take over the entire system.
The situation highlights a recurring tension in the cybersecurity world: the balance between coordinated disclosure and “full disclosure.” Normally, researchers give vendors a window (often 90 days) to fix a bug before making it public. By releasing the PoC and source code immediately, Chaotic Eclipse has significantly shortened the window for users to protect themselves and provided a blueprint for malicious actors.
| Exploit Name | Primary Impact | Target Component |
|---|---|---|
| MiniPlasma | SYSTEM Privilege Escalation | Cloud Filter Driver (cldflt.sys) |
| YellowKey | BitLocker Bypass | TPM-only Configurations |
| BlueHammer | Privilege Escalation | Windows Kernel/Local |
| UnDefend | Denial of Service | Windows Defender |
Microsoft has previously stated that it supports coordinated vulnerability disclosure and remains committed to investigating reported security issues to protect its customers. However, the existence of MiniPlasma suggests that “fixed” does not always mean “gone.”
The next critical checkpoint for users will be the upcoming Patch Tuesday cycle. Security administrators should monitor official Microsoft Security Response Center (MSRC) updates for any mentions of the Cloud Filter driver or new CVEs related to privilege escalation. Until a verified patch is deployed, the most effective defense remains a strategy of “least privilege,” ensuring that users do not run daily tasks with administrative rights.
Do you think bug bounty programs are doing enough to protect researchers, or is “full disclosure” the only way to force corporate accountability? Let us know in the comments.
