SignDrop: Public PoC Targets CLFS in Windows, Microsoft Has Yet to Release a Fix
The publicly available SignDrop project claims local privilege escalation through the CLFS mechanism in Windows. As of November 13, 2026, Microsoft had not published a CVE, advisory, or fix.
The SignDrop CLFS project, published in the GitHub repository of the MSNightmare account, claims local privilege escalation in Windows through the Common Log File System (CLFS) and Microsoft Defender. The author describes it as a “Windows Common Log FileSystem Authentication 0day Local Privilege Escalation Vulnerability.” As of November 13, 2026, Microsoft had not published a CVE, security advisory, or fix related to the case.
This is not a confirmed remote method of gaining access to a device. If the PoC’s claimed behavior were confirmed, an attacker would first need the ability to execute code on the system as a regular local user. They could then elevate privileges to the NT AUTHORITY\SYSTEM account.
What SignDrop CLFS Claims
The project’s source code is publicly available on GitHub. According to SecurityWeek, the PoC was compiled and tested by Cyderes. As of November 13, 2026, however, there was no evidence that SignDrop had been used in real-world attacks.
Microsoft has not yet publicly confirmed the technical mechanism or successful acquisition of SYSTEM privileges. Information about how the exploit works therefore comes primarily from the PoC author’s claims and a secondary description of its testing. Independent reproductions on supported Windows releases had not yet been confirmed in the available materials.
The author also estimates that approximately 80% of Windows installations may be vulnerable, or all systems updated more than 90 days ago. This estimate is not independently substantiated and cannot be considered a confirmed scope of exposure.
CLFS Authentication and .cnpf Files
CLFS is a Windows mechanism designed to work with log files. Microsoft states in its documentation that logfile authentication uses HMAC and creates an accompanying file with the .cnpf extension. Configuration modes in the registry may determine whether protection is enforced, learning mode is enabled, or protection is disabled.
SignDrop specifically targets this log-integrity protection mechanism. No official workaround or fix is currently known for SignDrop.
What Administrators Should Monitor
Because this is an alleged local privilege escalation, the most relevant context is one in which someone has already gained the ability to execute code on the device. Organizations should monitor Microsoft’s statements and any release of a CVE, fix, or mitigation.
- assignment of a CVE and a security advisory from Microsoft,
- independent reproductions of the PoC on supported Windows versions,
- credible information about any exploitation in real-world attacks,
- changes to Microsoft Defender detections and recommendations for enterprise environments.
Until an official statement is issued, SignDrop’s scope and practical reliability remain unclear. What is confirmed is the public release of the source code and the fact that Microsoft has not yet published a fix or advisory tied to this project.
Sources
- GitHub – MSNightmare/SignDrop – Confirms the public release of the SignDrop project and the author’s description of the PoC as a CLFS local privilege escalation.
- Microsoft Learn – CLFS logfile authentication – Confirms how CLFS authentication works, the .cnpf files, and the protection configuration modes.
- SecurityWeek – Corroborates the description of the public PoC, reports testing by Cyderes, and the absence of evidence of exploitation in the wild.
Verified and updated: November 13, 2026, 15:23
