CVE-2010-5248 in UltraVNC
Summary
by MITRE
Untrusted search path vulnerability in UltraVNC 1.0.8.2 allows local users to gain privileges via a Trojan horse vnclang.dll file in the current working directory, as demonstrated by a directory that contains a .vnc file. NOTE: some of these details are obtained from third party information.
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Analysis
by VulDB Data Team • 12/13/2021
The vulnerability identified as CVE-2010-5248 represents a critical untrusted search path weakness in UltraVNC version 1.0.8.2 that enables local attackers to escalate privileges through malicious DLL injection techniques. This flaw resides in the software's dynamic link library loading mechanism where the application fails to properly validate the source and integrity of loaded modules, creating an exploitable condition that can be leveraged by adversaries positioned within the same system.
The technical implementation of this vulnerability stems from improper handling of dynamic library loading sequences within the UltraVNC application framework. When the software processes .vnc configuration files, it attempts to load language-specific DLL modules without performing adequate path validation or integrity checks. The system searches for required libraries in a predetermined order that includes the current working directory, allowing a malicious actor to place a crafted vnclang.dll file in the same directory as a legitimate .vnc file, thereby causing the application to execute attacker-controlled code with the privileges of the victim user.
This vulnerability directly maps to CWE-426 Untrusted Search Path, which specifically addresses the dangerous practice of allowing applications to load libraries from untrusted locations without proper validation. The attack vector exploits the principle of least privilege by enabling local users to execute arbitrary code within the context of the running UltraVNC process, potentially leading to full system compromise. The operational impact extends beyond simple privilege escalation as the malicious DLL could be designed to establish persistent backdoors, exfiltrate sensitive data, or perform additional malicious activities.
The exploitation scenario demonstrates a classic Trojan horse attack pattern where the attacker places the malicious component in a location where the vulnerable application will automatically load it. This approach aligns with ATT&CK technique T1036.005 Masquerading and T1059.001 Command and Scripting Interpreter, as the malicious DLL can masquerade as legitimate system components while executing unauthorized operations. The vulnerability affects systems where UltraVNC is installed and where users have the ability to create or modify files in directories containing .vnc configuration files, making it particularly dangerous in multi-user environments where privilege separation is not properly enforced.
Organizations should implement immediate mitigations including updating to patched versions of UltraVNC, implementing proper file permissions on directories containing .vnc files, and conducting security audits to identify and remove vulnerable installations. System administrators should also consider implementing application whitelisting policies that restrict which DLLs can be loaded by the UltraVNC application, and deploy monitoring solutions to detect suspicious file creation patterns in directories where .vnc files are commonly stored. The vulnerability highlights the importance of secure coding practices and proper library loading mechanisms in preventing privilege escalation attacks that exploit trust relationships within software applications.