CVE-2016-5793 in Active OPC Server
Summary
by MITRE
Unquoted Windows search path vulnerability in Moxa Active OPC Server before 2.4.19 allows local users to gain privileges via a Trojan horse executable file in the %SYSTEMDRIVE% directory.
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Analysis
by VulDB Data Team • 04/24/2019
The vulnerability identified as CVE-2016-5793 represents a critical unquoted search path weakness in Moxa Active OPC Server versions prior to 2.4.19, which creates a significant privilege escalation vector for local attackers. This flaw stems from the software's failure to properly quote directory paths in its search mechanism, allowing malicious actors to place Trojan horse executables in strategic locations within the Windows file system hierarchy. The vulnerability specifically targets the %SYSTEMDRIVE% directory, which serves as a critical system location where legitimate applications and services expect to find executable files. When the vulnerable application attempts to locate and execute required components, it follows an insecure search path that does not properly validate or quote directory names containing spaces, thereby enabling attackers to intercept execution flow.
The technical implementation of this vulnerability aligns with CWE-428, which describes the weakness of unquoted search paths in Windows environments, and demonstrates how improper path handling can lead to arbitrary code execution. Attackers exploit this by placing malicious executables with the same names as legitimate application components in the %SYSTEMDRIVE% directory, where the vulnerable application will execute them instead of the intended legitimate files. This type of attack falls under the ATT&CK technique T1036.004, which covers masquerading through the use of legitimate system tools and services, and represents a classic example of a privilege escalation attack that leverages path traversal vulnerabilities. The vulnerability's impact is particularly severe because it operates at the local user level, requiring no network access or complex exploitation techniques, making it highly attractive to threat actors who seek to establish persistent access to compromised systems.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it enables attackers to establish persistent footholds within compromised environments while maintaining low detection rates. The attack requires minimal sophistication and can be executed through simple file placement operations, making it accessible to attackers with basic technical knowledge. Once exploited, the malicious executable gains the same privileges as the vulnerable application, potentially allowing attackers to execute arbitrary commands, modify system configurations, or establish backdoors. The vulnerability's persistence is enhanced by the fact that the %SYSTEMDRIVE% directory is commonly used for system-level operations and is often overlooked during security audits, creating a stealthy attack vector that can remain undetected for extended periods. Organizations utilizing Moxa Active OPC Server versions prior to 2.4.19 face significant risk exposure, particularly in industrial control environments where such servers may run with elevated privileges and control critical infrastructure components.
Mitigation strategies for CVE-2016-5793 focus on both immediate patching and defensive configuration measures to prevent exploitation. The primary remediation involves upgrading to Moxa Active OPC Server version 2.4.19 or later, which includes proper path quoting mechanisms that eliminate the vulnerability. Organizations should also implement strict access controls on the %SYSTEMDRIVE% directory and other critical system locations, ensuring that only authorized personnel can place executable files in these directories. Additional defensive measures include implementing application whitelisting policies, conducting regular security audits of system directories, and monitoring for unusual file placement activities in system drives. The implementation of these controls aligns with ATT&CK techniques T1562.001, which addresses privilege escalation through the manipulation of system components, and supports broader cybersecurity frameworks such as the NIST Cybersecurity Framework. System administrators should also consider deploying endpoint detection and response solutions that can identify suspicious file placement patterns and unauthorized executable installations, providing additional layers of protection against this and similar path traversal vulnerabilities.