Modern Operating Systems (OSs) enable user processes to obtain full access control over other processes initiated by the same user. In scenarios of sensitive security processes (e.g., antivirus software), protection schemes are enforced at the kernel level such as to confront arbitrary user processes overtaking with malicious intent. Within the Windows family of OSs, the kernel driver is notified via dedicated routines for user-mode processes that require protection. In such cases the kernel driver establishes a callback mechanism triggered whenever a handle request for the original user-mode process is initiated by a different user process. Subsequently, the kernel driver performs a selective permission removal process (e.g., read access to the process memory) prior to passing a handle to the requesting process. In this paper we are the first to demonstrate a fundamental user-mode process access control vulnerability, existing in Windows 7 up to the most recent Windows 10 OSs. We show that a user-mode process can indeed obtain a fully privileged access handle before the kernel driver is notified, thus prior to the callback mechanism establishment. Our study shows that this flaw can be exploited by a method to (i) disable the anti-malware suite Symantec Endpoint Protection; (ⅱ) overtake VirtualBox protected processes; (ⅲ) circumvent two major video game anti-cheat protection solutions, Bat-tlEye and EasyAntiCheat. Finally we provide recommendations on how to address the discovered vulnerability.
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