Security researcher Abdelhamid Naceri, known as Nightmare Eclipse, has released SignDrop, a Windows exploit that abuses a log-file security safeguard to elevate a standard user account to SYSTEM privileges. Cyderes’ Howler Cell team says it reproduced that escalation in a controlled test and dates the public proof-of-concept release to November 10, 2026. SourceSource
This is local privilege escalation: an attacker must already be able to run code on the machine. SignDrop can then raise that access to SYSTEM, Windows’ own highly privileged account. The reports do not describe a way to break into a PC directly over the internet. SourceSource
No Microsoft patch had been released as of November 12, according to CybSec World. Separately, Cyderes reported no confirmed exploitation in real-world attacks as of November 10. SourceSource
The signing step supplies the opening
Windows’ Common Log File System, or CLFS, handles logs. Its authentication feature is intended to detect unauthorized changes to log data. According to Cyderes, SignDrop leaves signed logs intact and instead abuses the creation of an associated .cnpf authentication file. SourceSource
In the reproduced chain, the exploit induces Microsoft Defender to open a prepared CLFS log under SYSTEM privileges. CLFS then creates an authentication file at an attacker-selected location, while leaving that file accessible to the attacker. The exploit replaces its contents with a malicious DLL—a code library—and arranges for that code to run. The result is a SYSTEM shell: a command window running with SYSTEM privileges. Source
The safeguard gets handed the wrong delivery address, and the attacker gets the benefit. Source
About that 80% figure
Naceri reportedly tested SignDrop on Windows 11 26H2, Windows 11 26H2 Experimental and Windows Server 2025 Experimental. Those reported tests are not a complete affected-version list. Cyderes also does not identify the Windows build used in its own controlled reproduction. SourceSource
The researcher estimates that 80% of Windows installations are vulnerable. Cyderes says no published data supports that figure. Source
Administrators can inventory CLFS authentication through the Mode value at HKLM\SYSTEM\CurrentControlSet\Services\CLFS\Authentication. Cyderes identifies 0 as enforcement mode and 1 as learning mode. Either meets one prerequisite identified by the researcher; neither setting alone establishes that exploitation will succeed. Source
Don’t pull out the safeguard
Cyderes advises against disabling CLFS authentication as a workaround, warning that doing so reopens exposure to older attacks that exploit memory-handling flaws. Swapping the new problem for the problems the safeguard was built to block is a miserable trade. Source
Instead, the team recommends restricting untrusted local code execution and keeping records of file creation, DLL loading and process activity. Those measures can limit opportunities for exploitation and preserve evidence; they do not fix the flaw. In Cyderes’ reproduction, the proof of concept removed its planted DLL while leaving the SYSTEM shell running, so a clean-looking directory afterward is not proof that nothing happened. Source
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