CVE-2018-18856 in LiquidVPN Client
Summary
by MITRE
Multiple local privilege escalation vulnerabilities have been identified in the LiquidVPN client through 1.37 for macOS. An attacker can communicate with an unprotected XPC service and directly execute arbitrary OS commands as root or load a potentially malicious kernel extension because com.smr.liquidvpn.OVPNHelper uses the system function to execute the "openvpncmd" parameter as a shell command.
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Analysis
by VulDB Data Team • 12/26/2024
The CVE-2018-18856 vulnerability represents a critical security flaw in the LiquidVPN client version 1.37 for macOS systems, exposing multiple local privilege escalation paths that can be exploited by malicious actors. This vulnerability stems from improper privilege management within the application's XPC service communication mechanisms, creating a dangerous attack surface that allows unauthorized users to execute arbitrary commands with root privileges. The flaw specifically affects the com.smr.liquidvpn.OVPNHelper component which utilizes a system function to execute the "openvpncmd" parameter as a shell command without proper input validation or sanitization. This design flaw creates a direct pathway for privilege escalation since the application fails to implement proper access controls or command injection protections when handling user-supplied parameters.
The technical implementation of this vulnerability demonstrates a classic command injection flaw that aligns with CWE-78, which specifically addresses improper neutralization of special elements used in OS commands. The vulnerability exists because the application directly passes user-controllable input to a system call without proper sanitization or parameter escaping, allowing an attacker to inject malicious commands that will be executed with elevated privileges. The XPC service communication channel lacks proper authentication mechanisms, making it accessible to unprivileged users who can then leverage this exposure to execute arbitrary commands. This particular flaw enables attackers to bypass normal access controls and escalate their privileges from standard user level to root level, providing complete system compromise capabilities.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it creates opportunities for persistent system compromise and data exfiltration. An attacker who successfully exploits this vulnerability can execute arbitrary code with root privileges, potentially installing malicious kernel extensions or modifying system files that would otherwise be protected. The ability to load malicious kernel extensions represents a particularly dangerous aspect of this vulnerability since kernel-level code operates with the highest privileges and can bypass all normal security mechanisms. This vulnerability also enables attackers to establish persistence mechanisms within the system, modify network configurations, or access sensitive data that would normally be protected from standard user access. The exposure affects all macOS systems running the vulnerable LiquidVPN client version, creating a widespread attack surface that could be exploited by any local user with access to the system.
Mitigation strategies for CVE-2018-18856 should focus on both immediate remediation and long-term architectural improvements. The most effective immediate solution involves updating to a patched version of the LiquidVPN client that properly validates and sanitizes all input parameters before executing system commands. Organizations should also implement network segmentation and access controls to limit local user privileges and prevent unauthorized access to potentially vulnerable applications. System administrators should consider disabling or removing the vulnerable XPC service if the application is not required, or implement additional monitoring to detect suspicious command execution patterns. The vulnerability also highlights the importance of proper input validation and privilege separation in application design, as outlined in the ATT&CK framework under privilege escalation techniques. Security teams should monitor for exploitation attempts through log analysis and implement network-based detection measures to identify potential command injection attempts. Additionally, the vulnerability serves as a reminder of the critical importance of secure coding practices and the need for regular security assessments of third-party applications, particularly those with elevated privileges or system-level access capabilities.