New SignDrop Zero-Day Exploit Turns Windows CLFS Security Feature Into SYSTEM Access
New SignDrop zero-day exploit allows local Windows users to gain SYSTEM privileges via CLFS driver.
A new local privilege escalation exploit named SignDrop targets a log-authentication feature in Windows' Common Log File System (CLFS) driver. The exploit abuses how clfs.sys creates companion files, using path redirection to allow a standard user to create a SYSTEM-level file, which can be chained into a SYSTEM shell. While Microsoft has not confirmed the flaw or released a fix, independent testing confirmed the exploit works, though it may not be reliable enough for operational use and requires Defender to be enabled.
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The lesson from this incident
Full lessonThe SignDrop exploit abuses a design flaw in Windows' Common Log File System (CLFS) driver, allowing a standard user to leverage path redirection during companion file creation to gain SYSTEM-level privileges. This is a zero-day, meaning no vendor patch currently exists, leaving organizations exposed with no straightforward remediation path. The vulnerability demonstrates how trusted OS components — particularly logging subsystems — can be weaponized to bypass security boundaries entirely. Organizations relying solely on vendor patching cycles are at significant risk during the gap between discovery and an official fix.
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- Automated patch management
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- Endpoint detection and response (EDR and XDR)
Malware and hands-on-keyboard attackers on laptops and servers get spotted and stopped.
Indicators of Compromise
Extracted by AI from the linked source. Not reviewed by an editor. How this works
- malware — SignDrop