CVE-2018-7716 in PrivateVPN
Summary
by MITRE
PrivateVPN 2.0.31 for macOS suffers from a root privilege escalation vulnerability with its com.privat.vpn.helper privileged helper tool. This privileged helper tool implements an XPC service that allows arbitrary installed applications to connect and send messages. The XPC service extracts the config string from the corresponding XPC message. This string is supposed to point to an internal OpenVPN configuration file. If a new connection has not already been established, an attacker can send the XPC service a malicious XPC message with the config string pointing at an OpenVPN configuration file that he or she controls. In the configuration file, an attacker can specify a dynamic library plugin that should run for every new VPN connection. This plugin will execute code in the context of the root user.
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Analysis
by VulDB Data Team • 01/10/2020
The vulnerability described in CVE-2018-7716 represents a critical privilege escalation flaw within PrivateVPN 2.0.31 for macOS systems. This security weakness stems from the implementation of a privileged helper tool named com.privat.vpn.helper which operates as an XPC service. The XPC service architecture allows for communication between applications and privileged processes, creating a potential attack surface when proper input validation and access controls are absent. The vulnerability specifically targets the helper tool's handling of configuration strings within XPC messages, which should normally reference internal OpenVPN configuration files. However, the implementation fails to properly validate or sanitize these configuration paths, creating an exploitable condition where malicious actors can manipulate the system's behavior through crafted XPC communications.
The technical exploitation of this vulnerability involves the attacker sending a specially crafted XPC message containing a malicious configuration string that points to an attacker-controlled OpenVPN configuration file. This configuration file can then specify a dynamic library plugin that executes code in the privileged root context during VPN connection establishment. The flaw demonstrates poor input validation practices and inadequate privilege separation mechanisms, allowing unprivileged applications to influence the execution of code with elevated privileges. This type of vulnerability aligns with CWE-20, "Improper Input Validation," and specifically manifests as a privilege escalation vector through improper access control mechanisms. The XPC service architecture itself is not inherently flawed, but the implementation lacks proper security controls to prevent arbitrary code execution in privileged contexts.
The operational impact of this vulnerability is severe as it allows attackers to gain root access to macOS systems running the affected PrivateVPN version. This privilege escalation capability enables comprehensive system compromise, including the ability to install persistent backdoors, modify system files, access all user data, and potentially escalate to network-wide control. The vulnerability is particularly dangerous because it requires no special privileges to exploit, making it accessible to any local user or application that can interact with the XPC service. Attackers can leverage this to perform reconnaissance, data exfiltration, or establish persistent access to compromised systems. The attack vector demonstrates characteristics consistent with ATT&CK technique T1068, "Exploitation for Privilege Escalation," where an adversary exploits a vulnerability in a privileged process to gain elevated system access.
Mitigation strategies for this vulnerability should focus on immediate patching of the PrivateVPN application to version 2.0.32 or later, which contains the necessary security fixes. System administrators should also implement monitoring for suspicious XPC service activity and network connections originating from the privileged helper tool. Additional protective measures include restricting the ability of applications to communicate with privileged XPC services through sandboxing policies and ensuring proper code signing validation. The vulnerability highlights the importance of secure XPC service implementation practices, including mandatory input validation, privilege separation, and proper access control enforcement. Organizations should also consider implementing application whitelisting policies to prevent unauthorized applications from interacting with privileged system components. This vulnerability serves as a reminder of the critical importance of secure coding practices in privileged system components and demonstrates how seemingly minor implementation flaws can result in catastrophic security consequences.