Ethical Hacking News
A critical Windows zero-day vulnerability has been identified, allowing local users to gain full System rights on some versions of Windows. The vulnerability, known as "SignDrop," exploits the interaction of CLFS, Windows Defender, and Windows file permissions. While Microsoft has introduced a security measure to prevent similar vulnerabilities, the "SignDrop" exploit can still be used to bypass antimalware engine defenses and gain elevated privileges. This article provides an in-depth look at the vulnerability, its impact, and the steps users can take to protect themselves.
Windows zero-day vulnerability "SignDrop" identified by Nightmare Eclipse, allowing local users to gain full System rights. The vulnerability resides in the Common Log File System (CLFS) and can be exploited by ordinary users to elevate privileges to System. The vulnerability can bypass self-defense mechanisms of antimalware engines, allowing attackers to trigger arbitrary file creation. The requirements for the vulnerability to work are Windows 26H2 and a system with a specific CLFS authentication mode value. The discovery highlights the importance of regular system updates, security patches, and user awareness of system configuration.
A critical Windows zero-day vulnerability, known as "SignDrop," has been identified by a disgruntled researcher, Nightmare Eclipse. This vulnerability allows local users to gain full System rights on some versions of Windows, including Windows 11 26H2 and Windows Server 2025 Experimental. The vulnerability resides in the Common Log File System (CLFS), a general-purpose logging service used by software clients running in user-mode or kernel-mode.
The attack exploits the interaction of CLFS, Windows Defender, and Windows file permissions. By forcing a privileged process such as Windows Defender to open a crafted CLFS container, an attacker with ordinary user rights can abuse the privileged file creation to elevate privileges to System. The vulnerability stems from a security measure introduced by Microsoft in October 2025 to prevent attackers from exploiting other vulnerabilities in CLFS.
Ironically, the vulnerability can be used against any antimalware engine to bypass their self-defense mechanism, allowing the attacker to trigger arbitrary file creation in the context of the antimalware process. This makes the vulnerability unique, as it can be used to turn off any antivirus/EDR. The researcher, Nightmare Eclipse, has published a proof-of-concept (PoC) for the exploit, which can be used to test if a system is vulnerable.
According to the researcher, Will Dormann, the requirements for the vulnerability to work are Windows 26H2, and one that has existed for more than 90 days. The HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CLFS\Authentication\Mode value must be 0 or 1 for a system to be vulnerable. Microsoft does staged rollouts of Windows updates, such as 26H2, so it's not clear how many people have it. A check can be done by running the "winver" command.
The discovery of this vulnerability highlights the ongoing cat-and-mouse game between security researchers and hackers. It also underscores the importance of regular system updates and security patches, as well as the need for users to be aware of their system's configuration and settings.
Related Information:
https://www.ethicalhackingnews.com/articles/Windows-0-Day-Vulnerability-Exposes-System-Rights-to-Hackers-ehn.shtml
https://arstechnica.com/security/2026/11/windows-0-day-dropped-by-disgruntled-researcher-hands-hackers-system-rights/
https://www.bleepingcomputer.com/news/security/new-windows-signdrop-zero-day-gives-hackers-system-privileges/
Published: Fri Nov 13 10:42:24 2026 by llama3.2 3B Q4_K_M
