CVE-2018-16156 in PaperStream IP
Summary
by MITRE
In PaperStream IP (TWAIN) 1.42.0.5685 (Service Update 7), the FJTWSVIC service running with SYSTEM privilege processes unauthenticated messages received over the FjtwMkic_Fjicube_32 named pipe. One of these message processing functions attempts to dynamically load the UninOldIS.dll library and executes an exported function named ChangeUninstallString. The default install does not contain this library and therefore if any DLL with that name exists in any directory listed in the PATH variable, it can be used to escalate to SYSTEM level privilege.
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Analysis
by VulDB Data Team • 10/14/2025
The vulnerability identified as CVE-2018-16156 resides within PaperStream IP (TWAIN) version 1.42.0.5685, specifically affecting the FJTWSVIC service component that operates with SYSTEM privileges on Windows systems. This service listens for unauthenticated messages through the FjtwMkic_Fjicube_32 named pipe, creating a potential attack surface where malicious actors can send crafted payloads to the service. The flaw manifests when the service processes these messages and attempts to dynamically load a library named UninOldIS.dll, which is not included in the default installation package. This dynamic loading behavior represents a classic security weakness where the service relies on the system's PATH resolution mechanism to locate required libraries, creating an opportunity for privilege escalation through DLL hijacking techniques.
The technical execution of this vulnerability involves the service's attempt to load the UninOldIS.dll library through a dynamic loading function, specifically calling an exported function named ChangeUninstallString. This function execution occurs within the context of the SYSTEM privilege, meaning any malicious code loaded through this mechanism will run with the highest level of system permissions. The vulnerability exploits the PATH environment variable resolution order where the system searches for libraries in the current directory first, followed by directories listed in the PATH variable, and finally in system directories. When the service attempts to load UninOldIS.dll, if a malicious version exists in any directory within the PATH, the system will load that malicious library instead of the legitimate one, allowing attackers to execute arbitrary code with SYSTEM privileges.
The operational impact of this vulnerability is significant as it enables local privilege escalation attacks that can be executed by any user with access to the system. The attack vector requires only that an attacker can place a malicious UninOldIS.dll file in a directory that appears earlier in the PATH environment variable than the legitimate system directories. This makes the vulnerability particularly dangerous because it can be exploited without requiring network connectivity or authentication, and the attack can be performed by any local user regardless of their privilege level. The vulnerability represents a critical weakness in the principle of least privilege, as the service's elevated privileges are unnecessarily exposed to potential manipulation through improper library loading practices.
This vulnerability aligns with CWE-426, which describes the insecure loading of dynamic libraries, and can be mapped to ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation'. The root cause stems from the service's failure to properly validate or restrict the library loading process, creating an environment where attackers can manipulate the dynamic loading behavior to achieve their objectives. Security best practices dictate that services running with elevated privileges should employ strict library loading mechanisms that either use absolute paths or implement proper validation of library sources. The vulnerability demonstrates the importance of implementing secure coding practices around dynamic library loading and the necessity of maintaining strict control over the PATH environment variable, particularly for system services that operate with elevated privileges. Organizations should implement mitigations including restricting the PATH variable, implementing proper DLL loading security controls, and ensuring that system services operate with minimal required privileges.