SignDrop proof of concept targets Windows CLFS authentication to gain SYSTEM
A researcher released a local privilege escalation proof of concept that uses CLFS authentication file creation and a privileged Defender operation. Testing was reported on selected Windows 11 26H2 and Windows Server 2025 builds.
- Disclosed
- Nov 10, 2026
- Public disclosure date
- Severity
- Sharted
- No CVE: a breach, not a bug
- Splash zone
- Windows hosts on which an attacker can run local code and CLFS authentication is in learning or enforcement mode, per the researcher.
- Windows · CLFS · privilege escalation
- In the wild
- Unknown
- Researcher proof of concept. The sources reviewed do not confirm attacks in the wild.
What happened
The researcher describes a file creation issue in clfs.sys. A standard local user sets up a CLFS log and associated container, then causes a privileged Defender operation to open it. The chain uses creation of a CLFS authentication file under a privileged context to demonstrate SYSTEM execution. The public notes name Windows 11 26H2, Windows 11 26H2 Experimental and Windows Server 2025 Experimental as test targets.
The mode test is a triage signal from the researcher. The available material does not establish all affected builds or an installed-base percentage. No Microsoft advisory assigning a CVE or a SignDrop-specific fixed build was verified in this review. Microsoft’s CLFS documentation describes the existing mitigation, including a learning period that begins when the system first starts with the relevant driver version. Microsoft documents values 2 and 3 as disabled modes. Keep current protections enabled while evaluating the researcher’s claims.
Crime-scene timeline
Nov 10, 2026
Researcher publishes SignDrop repository and technical notes
The public repository history records publication on November 10 UTC. The researcher reports a local path to SYSTEM.
Who said what
We list each claim and who made it. Primary sources (the vendor, the researcher, the registry) are marked. Where reports disagree, we grade by the worst credible case.
- SignDrop researcher repositoryPrimaryProvides the reported attack chain, prerequisites and testing claims.
- Microsoft CLFS authentication documentationPrimaryDefines mode values and explains the purpose of the protection.