SignDrop is a public exploit that can allow a local user to escalate their privileges to SYSTEM on Windows by exploiting how the CLFS logging system creates authentication files. The published research tested it on Windows 11 26H2 and experimental versions of Windows 11 and Windows Server 2025; Microsoft told SecurityWeek it is investigating the flaw, that Defender detects and blocks the exploitation, and that it has not observed attacks in the wild. Check the CLFS mode, but do not run the PoC.
Who may be affected and how to check
The vulnerability, named SignDrop by its author, Abdelhamid Naceri, known as Nightmare Eclipse, revolves around CLFS, the Windows subsystem that manages logs. The exploit prepares log files and tries to get a privileged process to open them; according to the technical explanation, the auxiliary authentication file may end up being created with SYSTEM permissions and retain permissions that allow the user who prepared it to modify it.
The check recommended by the researcher and coverage from The Hacker News and BleepingComputer is to read the Mode value at this Registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CLFS\Authentication\ModeValues 0 and 1 indicate exposure according to the scope described for SignDrop: they correspond to the authentication learning and enforcement modes. The Hacker News notes that systems usually switch from learning mode to enforcement mode after 90 days. Values 2 and 3 are outside the described attack, but are not a recommended solution: disabling the mitigation allows CLFS to process tampered logs again and may expose the device to memory corruption vulnerabilities.
The published tests were conducted on Windows 11 26H2, Windows 11 26H2 Experimental, and Windows Server 2025 Experimental. Naceri estimates that the flaw affects a large share of Windows installations, but that figure is his estimate, not an independent measurement. SecurityWeek also reports that Cyderes compiled and tested the PoC; an independent assessment cited by The Hacker News found that the exploit works, though not reliably enough for operational use.
What to do now
Read the value without changing it. Open Registry Editor and navigate to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CLFS\Authentication; check theModedata. If you are not experienced with the Registry, ask the device administrator for help rather than editing keys. The check should be limited to seeing whether the value is 0, 1, 2, or 3.If the value is 0 or 1, treat the device as exposed. This does not mean the system has been attacked: it indicates that it matches the modes the researcher considers vulnerable. On managed devices, report the value to the security or IT team responsible so they can assess the device and monitor Microsoft updates.
Keep the CLFS mitigation enabled. Do not change the value to 2 or 3 in an attempt to block SignDrop. Although those modes are outside the published attack, both the researcher and the cited documentation warn that disabling authentication stops protecting against tampered logs and the memory corruption flaws the mitigation is intended to contain.
Keep Microsoft Defender enabled. The published PoC chain requires Defender to be active, according to The Hacker News. SecurityWeek reports that Microsoft says Defender detects and blocks the exploitation and alerts on privilege escalation behavior. Do not disable antivirus or tamper protection to test the flaw.
Install official Windows updates when they become available and follow Microsoft's security update guidance. The November updates cited by The Hacker News did not include a patch for SignDrop. SecurityWeek reported that Microsoft was investigating the vulnerability; therefore, based on this information, there is no specific fix to install or patched version to recommend.
Escalate any alert or suspicious activity to your organization's administrator or security team. The published information does not confirm real-world SignDrop attacks, and Microsoft told SecurityWeek it had not observed exploitation in the wild. The absence of observed cases does not mean a specific device is clean if there are other signs of compromise.
Mistakes that can make the situation worse
Do not run the test exploit on your computer to find out whether it is vulnerable. BleepingComputer reports that Naceri suggests using the PoC or checking the Registry, but checking the value avoids running exploit code. In addition, The Hacker News warns that the published PoC may change UAC prompts to open a standard user console and a SYSTEM console, blocking other actions and making the test visible.
Do not confuse “outside the PoC's scope” with “safer.” Values 2 and 3 disable the CLFS authentication mitigation; the mechanism itself was introduced to limit attacks against driver vulnerabilities. Disabling this protection trades one risk for another; it does not fix SignDrop.
Also, do not assume that every antivirus product is protected against this technique. Naceri claims it could affect antimalware engines with privileged processes, but The Hacker News notes that this broader possibility has not been tested. The published chain uses Defender; Microsoft says its product detects and blocks the exploitation.
Finally, do not interpret the publication of a PoC as proof of ongoing attacks, or the lack of reports as a guarantee of safety. The available information describes a local risk that can escalate privileges and a Microsoft response that is still under investigation. For users, the practical step now is to check Mode without changing it and wait for an official fix.
Sources: BleepingComputer, The Hacker News, SecurityWeek, GitHub
