CVE-2018-16190 in UNARJ32.DLL
Summary
by MITRE
Untrusted search path vulnerability in UNARJ32.DLL for Win32, LHMelting for Win32, and LMLzh32.DLL (UNARJ32.DLL for Win32 Ver 1.10.1.25 and earlier, LHMelting for Win32 Ver 1.65.3.6 and earlier, LMLzh32.DLL Ver 2.67.1.2 and earlier) allows an attacker to gain privileges via a Trojan horse DLL in an unspecified directory.
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Analysis
by VulDB Data Team • 05/10/2020
This vulnerability represents a classic untrusted search path flaw that affects multiple compression and decompression libraries for win32 systems. The affected components include UNARJ32.DLL for Win32 version 1.10.1.25 and earlier, LHMelting for Win32 version 1.65.3.6 and earlier, and LMLzh32.DLL version 2.67.1.2 and earlier. These libraries are commonly used for handling archive files and decompression operations within windows environments, making them critical components in many software applications and system processes. The vulnerability stems from the improper handling of dynamic library loading sequences where these libraries search for required DLL dependencies in a predictable but insecure order that includes current working directories and user-writable locations.
The technical implementation of this vulnerability allows attackers to place malicious DLL files in directories that these libraries will search before checking system directories, enabling privilege escalation through a Trojan horse attack vector. This type of vulnerability falls under CWE-426 Untrusted Search Path, which specifically addresses the issue where applications search for libraries in insecure locations that can be manipulated by attackers. The flaw operates at the operating system level where dynamic link libraries are resolved through a specific search order that prioritizes user directories over system directories, creating an exploitable condition where attackers can insert malicious code that will execute with the privileges of the victim process.
The operational impact of this vulnerability extends beyond simple code execution to include full system compromise capabilities. When an application using these vulnerable libraries loads a malicious DLL, the attacker gains the same privileges as the running process, which could range from standard user access to system administrator privileges depending on the application context. This vulnerability is particularly dangerous because it can be exploited through various attack vectors including malicious archive files, email attachments, or compromised websites that trigger the loading of these vulnerable libraries. The attack requires minimal user interaction and can be automated, making it a significant threat to enterprise environments where these libraries might be used in critical applications or system tools.
Mitigation strategies for this vulnerability should focus on immediate patching of affected libraries to versions that implement secure library loading practices, which aligns with ATT&CK technique T1059 Command and Scripting Interpreter and T1546 Privilege Escalation. System administrators should also implement application whitelisting policies to prevent unauthorized DLL loading, utilize secure coding practices that avoid insecure search paths, and conduct regular security assessments of applications using these libraries. Additionally, implementing proper directory permissions and monitoring for suspicious DLL placement activities can help detect and prevent exploitation attempts. The vulnerability demonstrates the critical importance of following secure coding guidelines and proper library loading practices, as outlined in industry standards such as the OWASP Secure Coding Practices and Microsoft's Secure Application Lifecycle guidelines, which specifically address the prevention of untrusted search path vulnerabilities in software development and deployment environments.