CVE-2016-6167 in PuTTY
Summary
by MITRE
Multiple untrusted search path vulnerabilities in Putty beta 0.67 allow local users to execute arbitrary code and conduct DLL hijacking attacks via a Trojan horse (1) UxTheme.dll or (2) ntmarta.dll file in the current working directory.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/01/2022
The vulnerability identified as CVE-2016-6167 represents a critical untrusted search path issue affecting PuTTY beta 0.67, a widely used SSH and telnet client for Windows systems. This flaw stems from the application's improper handling of dynamic link library (DLL) loading mechanisms, creating opportunities for privilege escalation and arbitrary code execution through malicious DLL hijacking techniques. The vulnerability specifically targets the application's reliance on the current working directory for DLL resolution, which violates fundamental security principles of secure coding practices and proper DLL loading procedures.
The technical exploitation of this vulnerability occurs when a local attacker places malicious DLL files named UxTheme.dll or ntmarta.dll in the same directory as the PuTTY executable. When PuTTY attempts to load these libraries during normal operation, the system's DLL search order mechanism loads the attacker-controlled malicious DLL instead of the legitimate system libraries. This behavior aligns with CWE-426, which describes the insecure loading of dynamic link libraries due to insufficient validation of the library path. The vulnerability demonstrates a classic DLL hijacking attack pattern where the attacker leverages the system's default search order to execute code with the privileges of the targeted user.
The operational impact of CVE-2016-6167 extends beyond simple privilege escalation, as it provides attackers with a persistent foothold within compromised systems. Attackers can execute arbitrary code with the privileges of the user running PuTTY, potentially leading to complete system compromise, data exfiltration, or further network lateral movement. The vulnerability is particularly concerning because it affects a commonly used network administration tool, making it attractive to attackers who seek to establish persistent access within enterprise environments. This weakness also correlates with ATT&CK technique T1059.001, which covers command and scripting interpreter usage, as the compromised PuTTY process could be leveraged to execute further malicious commands.
Mitigation strategies for this vulnerability require immediate patching of PuTTY to version 0.68 or later, which addresses the untrusted search path issue through proper DLL loading mechanisms. Organizations should implement application whitelisting policies to restrict execution of unauthorized DLLs and conduct regular security assessments of critical network tools. System administrators should also monitor for suspicious DLL files in common application directories and implement proper file system permissions to prevent unauthorized DLL placement. The vulnerability highlights the importance of following secure coding practices such as those recommended in the OWASP Secure Coding Practices, particularly regarding the proper handling of dynamic library loading and the implementation of secure search paths that do not rely on the current working directory for critical system components.