A researcher has published SignDrop, a proof-of-concept exploit that reportedly lets a local Windows user gain SYSTEM privileges by abusing a security measure built to protect Windows log files. Security Affairs reported on November 13 that the researcher, known as Chaotic Eclipse, released code and a technical explanation on GitHub, describing a way to make Windows Defender create files with Windows’ highest system privileges.
The reported attack requires a local user to prepare files and cause a more privileged process to open them. The researcher tested the proof of concept on Windows 11 26H2, Windows 11 26H2 Experimental and Windows Server 2025 Experimental, and claims the technique could also bypass antivirus and endpoint detection and response (EDR) tamper protections. Those broader claims go beyond the named test configurations.
A protection mechanism becomes the attack path
SignDrop targets the Common Log File System (CLFS), a Windows component that processes log files in the kernel, the privileged core of the operating system. Its handling of complex files has made it a recurring target for memory corruption vulnerabilities.
Microsoft began rolling out CLFS authentication to the public release channel on October 28, 2025. The protection starts with a 90-day learning period, then requires log files to carry a valid authentication code.
The reported flaw concerns how the CLFS driver, clfs.sys, creates a .cnpf authentication file for a new log container. When a process creates its own log files, CLFS uses OBJ_FORCE_ACCESS_CHECK to enforce permissions in that process’s security context. But opening a log file also opens its associated container. If the associated file is empty, CLFS attempts to sign it, even if a signature file already exists.
That becomes exploitable when a privileged process opens a file prepared by a standard user. In the published technique, the researcher calls ServerMpUpdateEngineSignature and changes symbolic links—references that redirect object lookups—in the Windows Object Manager. This steers Defender’s antimalware engine into opening the CLFS container.
Defender then follows the associated file path and, when a signature is absent, creates one with SYSTEM privileges. CLFS applies the original file’s discretionary access control list, or DACL, which defines who can access the new file. The chain reportedly gives the attacker a route to higher privileges.
The researcher also argues that file creation performed inside an antimalware product’s own process can pass that product’s self-defense checks. On that basis, he claims SignDrop could disable antivirus or EDR protections across other products.
Exposure guidance contains conflicting descriptions
Chaotic Eclipse estimates that roughly 80% of Windows installations may be affected, but the account gives conflicting descriptions of the relevant 90-day window: his quoted GitHub statement identifies installations older than 90 days as generally vulnerable, while the article’s explanation points to systems still learning or with protection only partly enabled.
The report gives a more specific configuration check: inspect HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CLFS\Authentication\Mode. It describes values 0 and 1 as vulnerable, and 2 and 3 as protected. Administrators can use that reported distinction to assess configuration, while treating the worldwide exposure estimate as the researcher’s claim.
The researcher, who recently identified himself as Abdelhamid Naceri, has previously published exploits targeting Microsoft Defender and other security products; Security Affairs says some earlier releases were later exploited in the wild.
Disabling CLFS authentication reportedly removes the SignDrop attack path, but also removes protection against the memory corruption attacks it was introduced to address. The researcher therefore describes disabling it as a tradeoff and says a Microsoft patch is needed to resolve the issue.
