Science & Tech · Cybersecurity · 1 hr ago
SignDrop exploit could give local Windows users SYSTEM access
Security researcher Abdelhamid Naceri released SignDrop, an exploit that could let someone already using a Windows computer gain its highest level of access, called SYSTEM.
It targets the Windows Common Log File System, which handles log files, and abuses how the system creates an authentication file when a privileged program opens a prepared log.
The exploit’s published method gets Windows Defender to open the prepared file, so Windows creates that companion file with SYSTEM privileges while retaining permissions the user can control.
Naceri estimates that about 80% of Windows installations may be vulnerable, but that figure has not been independently established across all systems.
Microsoft has not confirmed the flaw or released a fix, and there is no evidence it has been used in real attacks.
Independent testers reported that the exploit works, but one assessment said it was not reliable enough for practical use; the published method also requires Defender to be enabled and can make the attack noticeable.
Disabling the CLFS protection is not a safe workaround, because it could expose Windows to the memory-corruption attacks the protection was designed to prevent.
The next step is for Microsoft to respond and, if it confirms the issue, provide a fix; the sources say users should not disable the mitigation.
A publicly released Windows exploit called SignDrop may let a local user gain SYSTEM privileges by abusing the Common Log File System driver.
The exploit targets the creation of a companion authentication file, which can be created with elevated privileges and redirected to a location controlled by the user.
The researcher says SignDrop was tested on Windows 11 26H2, an experimental Windows 11 build and an experimental Windows Server 2025 build.
The researcher estimates that 80% of Windows installations may be vulnerable, while an independent assessment reported that the exploit did not run reliably enough for operational use.
Microsoft has not confirmed the flaw or released a fix, and one report says there is no evidence it has been exploited in the wild.
- Who
- Security researcher Abdelhamid Naceri, who publishes under the name Nightmare Eclipse, released the exploit.
- What
- SignDrop may let a local Windows user gain SYSTEM privileges by exploiting the CLFS driver.
- When
- The public exploit code was released on Tuesday, November 10, 2026.
- Where
- The claimed vulnerability affects Windows systems using the Common Log File System.
- Why
- The exploit abuses how CLFS creates a companion authentication file when a privileged process opens a prepared log.
This story does not have two clearly opposing sides.
Microsoft shipped CLFS log-authentication updates for Windows 11 25H2, 26H1 and Windows Server 2025.
Naceri released SignDrop code and a detailed write-up on GitHub.
78researchlab published an assessment saying the exploit worked but did not run reliably enough for operational use.
- Exploit
- SignDrop
- Target component
- Windows Common Log File System driver, clfs.sys
- Companion file
- .cnpf
- Tested systems
- Windows 11 26H2, Windows 11 26H2 Experimental, and Windows Server 2025 Experimental
- Researcher's estimate
- 80% of Windows installations may be vulnerable
- Independent assessment
- 78researchlab said the exploit worked but was not reliable enough for operational use
4 sources
What people are saying
Everything is done properly by Microsoft here but the logic allows abuse
If everything is chained correctly, funnily, this legit security mitigation can be used against itself and allow an elevation of privileges.
What makes it funnier is the fact that it can be used against any antimalware engine to bypass their self defense (or tamper protection) mechanism, as you can trigger arbitrary file creation in the context of their own antimalware process so from the perspective of their kernel drivers, the file creation request is coming from their own legit process so it passes, this makes this vulnerability unique as it can be used to turn off any antivirus/EDR.