Ethical Hacking News
A new zero-day exploit has been discovered in the Windows Common Log File System (CLFS) driver, which can be used to gain SYSTEM privileges and potentially escalate to a SYSTEM shell. The exploit, dubbed "SignDrop," targets a recently added authentication check in the CLFS driver, which was intended to enhance the security of the system. This is a critical vulnerability that requires immediate attention from system administrators and security experts.
A new zero-day exploit, dubbed "SignDrop," has been discovered in the Windows Common Log File System (CLFS) driver, which allows a local user to gain SYSTEM privileges.The exploit targets a recently added authentication check in the CLFS driver, which was intended to enhance security, but has been found to be vulnerable.The vulnerability is classified as a "local privilege escalation" vulnerability, which means an attacker does not need admin privileges to exploit it.The exploit works on Windows 11 26H2, Windows 11 26H2 Experimental, and Windows Server 2025 Experimental, but can be chained into a SYSTEM shell on any version of Windows.Microsoft has not confirmed the claimed flaw, assigned a CVE, or released a fix, leaving system administrators and security experts to take immediate action.
A new, critical zero-day exploit has been discovered in the Windows Common Log File System (CLFS) driver, a logging subsystem built into the operating system. The exploit, dubbed "SignDrop," targets a recently added authentication check in the CLFS driver, which was intended to enhance the security of the system. However, the researchers behind the exploit have found a way to abuse this feature, allowing a local user to gain SYSTEM privileges and potentially escalate to a SYSTEM shell.
The exploit was discovered by researcher MSNightmare, who published the code and a detailed write-up on GitHub. According to the researchers, the exploit works by creating a companion file (.cnpf) that is created with the same security attributes as the original log file. However, by manipulating the creation of this file, an attacker can redirect the file creation to a location of their choosing, effectively taking control of the operation. This allows the attacker to write to the file as SYSTEM, which can then be chained into a SYSTEM shell.
The researchers noted that the logic behind the exploit is proper, as Microsoft has implemented several security measures to prevent this type of attack. However, the exploit still manages to find a way around these measures, making it a significant concern for system administrators and security experts.
The vulnerability is attributed to the CLFS driver's authentication feature, which was added to the driver last year. The feature uses a hash-based message authentication code (HMAC) to verify the integrity of the log file. However, the researchers found that an attacker can manipulate the HMAC to create a tampered log file that can be parsed by the driver.
The vulnerability is classified as a "local privilege escalation" vulnerability, which means that an attacker does not need to have administrative privileges to exploit it. The vulnerability is also considered "high-severity," as it can be used to gain SYSTEM privileges and potentially escalate to a SYSTEM shell.
The researchers noted that the exploit works on Windows 11 26H2, Windows 11 26H2 Experimental, and Windows Server 2025 Experimental. However, they also noted that the vulnerability is not limited to these versions, as it can be chained into a SYSTEM shell that can run on any version of Windows.
The researchers have released a proof-of-concept code for the exploit, which can be used by researchers and security experts to test the vulnerability. However, they also noted that the code is not intended to be used for malicious purposes and should only be used for testing and research purposes.
In response to the discovery, Microsoft has not confirmed the claimed flaw, assigned a CVE, or released a fix. The company has published its November security updates, which include a patch for a different vulnerability. However, the researchers noted that the patch does not address the SignDrop vulnerability.
System administrators and security experts are advised to check their exposure by reading the CLFS authentication mode at HKLM\SYSTEM\CurrentControlSet\Services\CLFS\Authentication. The vendor's mitigation guidance describes the setting and the risks of disabling it. The researchers also noted that the exploit can be chained into a SYSTEM shell that can run on any version of Windows, making it a significant concern for system administrators and security experts.
In conclusion, the SignDrop zero-day exploit is a critical vulnerability that can be used to gain SYSTEM privileges and potentially escalate to a SYSTEM shell. The exploit targets a recently added authentication check in the CLFS driver, which was intended to enhance the security of the system. However, the researchers behind the exploit have found a way to abuse this feature, allowing a local user to gain SYSTEM privileges. System administrators and security experts are advised to take immediate action to address this vulnerability and prevent potential attacks.
Related Information:
https://www.ethicalhackingnews.com/articles/New-SignDrop-Zero-Day-Exploit-Turns-Windows-CLFS-Security-Feature-Into-SYSTEM-Access-ehn.shtml
https://thehackernews.com/2026/11/new-signdrop-zero-day-exploit-turns.html
Published: Thu Nov 12 13:19:34 2026 by llama3.2 3B Q4_K_M
