CVE-2018-6947 in NoMachine
Summary
by MITRE
An uninitialised stack variable in the nxfuse component that is part of the Open Source DokanFS library shipped with NoMachine 6.0.66_2 and earlier allows a local low privileged user to gain elevation of privileges on Windows 7 (32 and 64bit), and denial of service for Windows 8 and 10.
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Analysis
by VulDB Data Team • 11/17/2025
The vulnerability identified as CVE-2018-6947 represents a critical security flaw within the nxfuse component of the Open Source DokanFS library that was distributed with NoMachine versions 6.0.66 and earlier. This issue manifests as an uninitialized stack variable within the kernel-mode driver component that handles file system operations, creating a potential pathway for privilege escalation attacks. The vulnerability specifically affects Windows 7 systems across both 32-bit and 64-bit architectures while also causing denial of service conditions on Windows 8 and 10 platforms, demonstrating the widespread impact of uninitialized memory access flaws in kernel drivers.
The technical root cause of this vulnerability stems from improper memory initialization within the nxfuse driver's stack-based memory allocation during file system operation processing. When the driver handles certain file system requests, it fails to properly initialize a stack variable before using its contents, creating a scenario where uninitialized memory values are processed as part of the privilege checking logic. This uninitialized data can contain arbitrary values from previous stack operations, potentially allowing an attacker to manipulate the driver's behavior to bypass security checks. The flaw aligns with CWE-457, which specifically addresses the use of uninitialized variables in security contexts, and represents a classic example of how improper memory management can create exploitable conditions in kernel-mode code.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass broader system stability concerns. On Windows 7 systems, a local low-privileged user can potentially leverage this uninitialized variable to elevate their privileges to system level, effectively compromising the entire system. This privilege escalation occurs because the uninitialized memory values can influence conditional logic within the driver's security validation routines, allowing attackers to manipulate the system's access control mechanisms. Additionally, the vulnerability causes denial of service conditions on Windows 8 and 10 systems, where the uninitialized stack variable can trigger system crashes or lockups during file system operations, rendering the affected systems unstable and potentially unusable.
From an attack perspective, this vulnerability follows the ATT&CK framework's privilege escalation techniques, specifically targeting the 'Exploitation for Privilege Escalation' and 'Memory Injection' tactics. The attack vector requires local system access but can result in complete system compromise, making it particularly dangerous in environments where users may have legitimate access to systems but should not possess administrative privileges. The exploitability is enhanced by the fact that the vulnerability exists in a widely used file system driver component, meaning that many systems in the wild could be potentially affected. Security researchers have noted that this type of uninitialized variable vulnerability is particularly challenging to detect through automated analysis tools due to the complex nature of kernel-mode memory management and the specific conditions required for exploitation.
The recommended mitigation strategy involves immediate patching of the NoMachine software to version 6.0.67 or later, which contains the necessary fixes for the uninitialized stack variable issue. Organizations should also implement additional security controls including user access restrictions, monitoring for unusual file system activity, and regular security assessments of third-party components. System administrators should consider implementing application whitelisting policies to restrict execution of potentially vulnerable components and ensure that all systems are updated with the latest security patches. The vulnerability highlights the critical importance of proper memory initialization practices in kernel-mode drivers and serves as a reminder of the potential consequences of inadequate security testing in system components that handle privileged operations.