CVE-2020-5180 in Viscosity
Summary
by MITRE
Viscosity 1.8.2 on Windows and macOS allows an unprivileged user to set a subset of OpenVPN parameters, which can be used to load a malicious library into the memory of the OpenVPN process, leading to limited local privilege escalation. (When a VPN connection is initiated using a TLS/SSL client profile, the privileges are dropped, and the library will be loaded, resulting in arbitrary code execution as a user with limited privileges. This greatly reduces the impact of the vulnerability.)
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Analysis
by VulDB Data Team • 01/15/2020
The vulnerability identified as CVE-2020-5180 resides within Viscosity version 1.8.2, a popular VPN client application for both Windows and macOS operating systems. This security flaw represents a local privilege escalation vulnerability that specifically targets the OpenVPN integration capabilities within the Viscosity software. The vulnerability exploits a design weakness in how the application handles OpenVPN parameter configuration, creating a pathway for unprivileged users to influence the execution environment of the OpenVPN process. The issue manifests when users attempt to establish VPN connections using TLS/SSL client profiles, which inherently involve privilege dropping mechanisms that create a window of opportunity for malicious code injection.
The technical exploitation mechanism involves the manipulation of OpenVPN parameters that control library loading behavior within the VPN connection process. When a user initiates a VPN connection through a TLS/SSL client profile, the OpenVPN process temporarily drops its elevated privileges to operate with reduced permissions. During this privilege dropping phase, the application loads external libraries specified in the OpenVPN configuration parameters, providing an opportunity for an unprivileged user to inject malicious code. This vulnerability specifically affects the library loading process and can be leveraged to execute arbitrary code within the context of the OpenVPN process, effectively enabling local privilege escalation. The CWE-426 weakness classification applies here as the application performs insecure library loading operations that allow attackers to influence which libraries are loaded.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it represents a significant security risk for environments where unprivileged users have access to systems running Viscosity. Attackers can exploit this flaw to execute malicious code with elevated privileges, potentially allowing them to establish persistent access, escalate privileges further, or access sensitive system resources. The vulnerability's limited scope means that while it provides local privilege escalation capabilities, the actual execution of arbitrary code requires specific conditions to be met, including the ability to manipulate OpenVPN configuration files and the presence of the vulnerable Viscosity version. The ATT&CK technique T1068 demonstrates how this vulnerability can be leveraged for privilege escalation, while T1546.001 addresses the specific mechanism of DLL side-loading that may be applicable to the library loading process.
Mitigation strategies for CVE-2020-5180 should prioritize immediate software updates to versions that address the vulnerability in the Viscosity application. Organizations should also implement strict access controls to prevent unprivileged users from modifying OpenVPN configuration files, particularly those that control library loading parameters. Security monitoring should focus on detecting unauthorized changes to VPN configuration files and unusual library loading activities. The implementation of application whitelisting policies can prevent the execution of unauthorized libraries, while regular security audits should verify that OpenVPN configuration parameters are properly secured. Additionally, system administrators should consider implementing network segmentation to limit the potential impact of privilege escalation exploits and ensure that VPN client configurations follow security best practices to minimize attack surface.