Overview
Inter-Process Communication (IPC) is simply the set of mechanisms that let two or more processes on the same machine exchange data or signals. Across Windows, Linux and macOS you’ll find pipes or FIFOs, shared memory regions, message queues and—crucially for many modern services—sockets (named pipes on Windows, UNIX Domain Sockets on Unix-like systems, and Mach ports/XPC on macOS). These primitives differ in performance and complexity, but they all serve the same goal: enable a less-privileged component (for example, a user-facing GUI) to invoke functionality in a more-privileged daemon (like a VPN manager).
In the modern network communication, VPN services often rely on advanced methods for inter-process communication (IPC) to manage their operations effectively. One common approach is the use of gRPC over Unix Domain Sockets, allowing different processes within the system to interact efficiently and securely. IPC allows a management service to enable, disable, and configure VPN tunnel settings on demand.
However, a critical misconfiguration can arise when the Unix Domain Socket used for these operations is granted write permissions to all users on the system. As a result, any local user or application - regardless of their authorization - can modify the VPN tunnel, such as enabling, disabling, or changing its settings, without the knowledge or consent of the current user. This issue becomes even more problematic in environments where multiple users operate on the same host, as one user could alter or disrupt another’s VPN connection without their awareness, raising serious security and privacy concerns.
Think of IPC as a local REST API: processes exchange JSON or binary messages over a socket rather than over TCP. In fact, plenty of system daemons (e.g. Docker, various VPN clients) expose HTTP-style endpoints on a UNIX socket, allowing you to curl –unix-socket commands just like you would against a webserver. But just as you’d lock down a public API with tokens or OAuth, IPC endpoints must be guarded—and most operating systems enforce this via filesystem permissions on the socket file (owner/group/mode). If a socket is world-writable or world-readable, any local user can connect and call methods that should be privileged: enabling, disabling or reconfiguring a VPN tunnel without the original user’s knowledge or consent. Properly scoping ownership and restricting access bits is therefore critical to prevent unauthorized local actors from hijacking internal APIs.
Proof of Concept
To demonstrate this vulnerability, I created custom software using Visual Studio and the provided client-side VPN management DLL. Below is the detailed method I used to exploit the discovered flaw.
Initially, I set up a new Visual Studio project and included the required DLL file (name and location redacted for security reasons) as a dependency. Next, I developed a small exploit application using C#:
Executing this exploit immediately disconnects the VPN tunnel without the victim’s knowledge. Furthermore, by altering the configuration in the code (such as setting a malicious DNS server), additional attacks become possible.
Potential impacts
This vulnerability exposes multiple risks. An attacker with local access, either directly or via malware, can disable or alter the VPN tunnel silently. Such unauthorized manipulation of VPN settings can lead to serious security incidents, including data interception, redirection of traffic to attacker-controlled servers, or denial of service for critical network resources.
In multi-user systems, one user’s legitimate VPN session could be silently modified by another user. The affected user receives no warning resulting in a false sense of security!
Recommendations and mitigation
To mitigate this vulnerability, I strongly recommend restricting socket access to the initiating user alone. The socket permissions should be tightly controlled to ensure no unauthorized users or applications can write commands to the VPN service.
Additionally, it is critical to implement system-level notifications for any change in the state of the VPN tunnel. Users must be informed whenever the tunnel status changes, particularly if the changes occur without explicit user intervention. Providing clear notifications will significantly reduce the risk of unnoticed manipulation of VPN configurations.
