CVE-2018-7715 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 path string from the corresponding XPC message. This string is supposed to point to PrivateVPN's internal openvpn binary. If a new connection has not already been established, an attacker can send the XPC service a malicious XPC message with the path string pointing at a binary that he or she controls. This results in the execution of arbitrary code as the root user.
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Analysis
by VulDB Data Team • 01/10/2020
The vulnerability identified as CVE-2018-7715 represents a critical privilege escalation flaw within PrivateVPN 2.0.31 for macOS systems. This security weakness stems from the improper implementation of a privileged helper tool named com.privat.vpn.helper which operates as an XPC service. The XPC service architecture allows for inter-process communication between unprivileged applications and privileged system components, creating a potential attack vector when proper input validation and sanitization mechanisms are absent. The vulnerability specifically manifests in the helper tool's handling of path strings extracted from XPC messages, where the system fails to adequately verify or sanitize the input before executing operations.
The technical exploitation of this vulnerability occurs through the manipulation of the XPC service's path string parameter, which is intended to reference PrivateVPN's internal openvpn binary. When a new connection is established, the privileged helper tool processes XPC messages containing path information, but fails to validate whether the specified path points to a legitimate system binary. An attacker can craft a malicious XPC message with a crafted path string that points to an executable controlled by the attacker, effectively bypassing normal privilege boundaries. This flaw enables arbitrary code execution with root privileges, as the XPC service executes the malicious binary with elevated permissions. The vulnerability demonstrates a classic improper input validation issue that falls under CWE-20, specifically related to the improper handling of input data within privileged execution contexts.
The operational impact of CVE-2018-7715 is severe and far-reaching, as it allows attackers to gain root access to macOS systems running the affected PrivateVPN version. This privilege escalation capability enables attackers to bypass system security controls, modify system files, install persistent backdoors, and access all user data without detection. The vulnerability affects the integrity and confidentiality of the entire system, as the attacker can manipulate the network security layer that PrivateVPN is designed to provide. The attack requires minimal prerequisites since any installed application can potentially communicate with the XPC service, making exploitation relatively straightforward. This type of vulnerability directly aligns with ATT&CK technique T1068, which covers 'Local Privilege Escalation' through the exploitation of system services and helper tools.
Mitigation strategies for this vulnerability should focus on immediate remediation through the installation of updated PrivateVPN software versions that address the improper input validation in the XPC service implementation. System administrators should also implement monitoring for suspicious XPC service activity and consider restricting communication between untrusted applications and privileged helper tools. The underlying security principle of least privilege should be enforced by ensuring that helper tools only accept validated input and perform proper path validation before executing any operations. Additionally, macOS security configurations should be reviewed to limit the exposure of privileged XPC services to untrusted applications. Organizations should conduct security assessments to identify other potentially vulnerable helper tools and XPC services within their systems, as similar patterns may exist in other applications. The vulnerability highlights the critical importance of secure coding practices for privileged system components and demonstrates the necessity of proper input validation even in trusted helper processes.