Researcher Releases SignDrop Windows Privilege Escalation Exploit

Security researcher Abdelhamid Naceri, known online as Nightmare Eclipse, has disclosed a Windows zero-day exploit named SignDrop that targets the Common Log File System (CLFS) and can push a local user’s privileges to the System level by abusing the way CLFS handles authentication during log-file creation. The PoC reportedly manipulates the creation/opening sequence for both a log file and its container; if the container is empty, CLFS will sign it regardless of whether a signature file exists.

The attacker then coerces Windows Defender to open the file within the antimalware process context via the signature update RPC interface, enabling a signature file to be created with System privileges and potentially a payload to be placed there to spawn a System shell. SecurityWeek notes that it has not itself tested SignDrop, but Cyderes says it successfully compiled and tested the PoC.

According to Naceri, SignDrop has been tested on Windows 11 26H2, Windows 11 26H2 Experimental, and Windows Server 2025 Experimental, and may affect about 80% of Windows installations. He further states that a standard user can create a log file and point a container path to trigger the attack, with the vulnerability primarily tied to older Windows systems (he suggests “older than 90 days” as generally vulnerable). SecurityWeek says there is no evidence the zero-day has been exploited in the wild, and Microsoft has not yet provided a public statement.