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New Windows SignDrop Zero-Day Gives Hackers SYSTEM Privileges
Abdelhamid Naceri says the flaw can force privileged processes to create files, and he estimates 80% of Windows installations are vulnerable.
- Security researcher Abdelhamid Naceri released SignDrop, a new Windows zero-day exploit that allows attackers to gain SYSTEM privileges by exploiting a flaw in the Common Log File System driver's authentication process.
- The vulnerability stems from a Microsoft security mitigation introduced in October 2025 to defend against authentication attacks. Naceri said "the logic allows abuse," as the mitigation can be turned against itself to facilitate privilege elevation.
- Approximately 80% of Windows installations are vulnerable, as the technique bypasses antimalware tamper protection by triggering file creation within a legitimate process context. Naceri recommends checking registry settings to determine exposure.
- Microsoft has not released a patch and warned that anyone engaging in "malicious activity causing real harm" could face legal action. Naceri advises waiting for an official fix, as disabling the mitigation would expose systems to memory corruption vulnerabilities.
- Naceri, a former Microsoft employee, has disclosed numerous other unpatched zero-day flaws this year, including ShieldBreak and RoguePlanet. The researcher's public disclosure approach has drawn company criticism and legal warnings from Microsoft.
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One researcher published SignDrop, a proof of concept that he claims takes advantage of a Windows mitigation to elevate privileges and could interfere with anti-virus self-protection. The case raises a paradox: the same defense designed to limit attacks against CLFS can open a way of abuse when a privileged process manipulates log files.
SignDrop Zero-Day Exploit Abuses CLFS To Gain Access
A newly published proof of concept, the SignDrop zero-day exploit, claims a standard local Windows user can gain SYSTEM privileges through the Common Log File System (CLFS) driver. Its author, MSNightmare, posted the code and a detailed writeup on GitHub on Tuesday, the same day Microsoft released its November security updates. Microsoft has not
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