New SignDrop Zero-Day Exploit Turns Windows CLFS Security Feature Into SYSTEM Access
Nov 12, 2026
Vulnerability / Endpoint Security
Public exploit code released earlier this week claims that a local Windows user can gain SYSTEM privileges through the Common Log File System driver. The proof of concept, called SignDrop , targets a log-authentication feature added to the driver last year. It abuses how clfs.sys creates companion files when a privileged process opens a prepared log, using path redirection to take control of the operation. Microsoft has not confirmed the claimed flaw, assigned a CVE, or released a fix. The researcher behind the exploit, who publishes under the name MSNightmare , released the code and a detailed writeup on GitHub on Tuesday, the same day the company published its November security updates. CLFS is a logging subsystem built into Windows. Its driver has been a frequent target for privilege escalation: 10 CLFS flaws appear in CISA's catalog of vulnerabilities known to have been exploited in attacks, including one used in ransomware campaigns in April 2025. To reduce that expo...