Are Open Source VPNs Safe?

The Security Advantage of Open Source

The core security argument for open source VPN software is verifiability. When a VPN provider claims their software uses AES-256 encryption, does not log user activity, and has no backdoors, there are exactly two ways to evaluate those claims: trust the company, or read the code. With closed-source VPNs, only the first option is available. With open source VPNs, anyone with the technical knowledge can independently verify every claim.

This is not a theoretical distinction. Multiple closed-source VPN services have been caught contradicting their own privacy policies. In 2020, a widely advertised "no-log" VPN provider suffered a data breach that revealed extensive user connection logs, including timestamps, source IP addresses, and bandwidth usage. The company had claimed in its marketing that it kept no logs of any kind. Had the software been open source, researchers could have identified the logging code before the breach exposed millions of users.

Open source VPN software benefits from a form of security review that closed-source products cannot match. WireGuard's approximately 4,000-line codebase has been reviewed by hundreds of independent security researchers, analyzed in multiple academic papers, and formally verified using symbolic analysis tools. When security researcher Jason Donenfeld submitted WireGuard for inclusion in the Linux kernel, it underwent review by the kernel development team, one of the most rigorous code review processes in software engineering. This level of scrutiny is only possible because the code is open.

Professional Security Audits

Beyond community review, the major open source VPN projects have commissioned professional security audits from independent firms.

OpenVPN was audited by Quarkslab on behalf of OSTIF (the Open Source Technology Improvement Fund) in 2017. The audit examined the OpenVPN 2.4 codebase and found two vulnerabilities, both of which were fixed before the audit results were published. The full audit report was released publicly, allowing anyone to review the findings and verify the fixes. OpenVPN has undergone additional security reviews since then as part of the development process for the 2.5 and 2.6 releases.

WireGuard has been the subject of multiple independent security analyses. Its Noise protocol handshake pattern was formally verified using Tamarin, a security protocol verification tool. The cryptographic design was analyzed in a 2018 academic paper that concluded the protocol met its security goals under standard cryptographic assumptions. The kernel implementation has been reviewed by both the Linux kernel security team and independent researchers.

ProtonVPN's client applications, including its Android, iOS, Windows, macOS, and Linux apps, were audited by SEC Consult in 2019 and again in subsequent years. All audit reports are published on ProtonVPN's website. Mullvad VPN has similarly published audit reports for its client applications, conducted by Cure53 and other independent security firms.

These audits are only possible, and only meaningful, because the code is open source. An audit of closed-source software typically involves a non-disclosure agreement that prevents the auditor from publishing findings, which means users must trust both the software vendor and the auditing firm. Open source audits, by contrast, produce public reports that anyone can read and evaluate.

Limitations of Open Source VPN Security

Open source is a necessary but not sufficient condition for security. Several factors can undermine the security of an open source VPN even though the code is publicly available.

First, code availability does not guarantee code review. A small open source VPN project with few contributors may have publicly available code that nobody has actually audited. The security benefit of open source scales with the size and engagement of the community. WireGuard and OpenVPN benefit from large, active communities and professional audits. A lesser-known open source VPN tool with 50 stars on GitHub may have bugs that no one has looked for.

Second, the VPN protocol is only one component of the security stack. Even a perfectly secure VPN implementation can be undermined by a misconfigured server, an outdated operating system, weak firewall rules, DNS leaks, or WebRTC leaks in the browser. Self-hosted VPN users are responsible for all of these components, and a mistake in any one of them can expose traffic that the VPN is supposed to protect.

Third, open source VPN software, like all software, can have vulnerabilities. The difference is how quickly those vulnerabilities are discovered and fixed. The OpenSSL Heartbleed vulnerability (2014) was a critical bug in an open source library used by OpenVPN and millions of other applications. It existed in the code for over two years before it was discovered. However, once found, the fix was developed and deployed rapidly because the code was open. An equivalent vulnerability in closed-source software could persist indefinitely without discovery.

Open Source vs Closed Source: The Evidence

Comparing the security track records of open source and closed source VPN products reveals a consistent pattern. Open source VPN projects disclose vulnerabilities publicly, fix them quickly, and publish detailed advisories. Closed-source VPN services frequently experience breaches that expose user data, often revealing logging practices that contradicted their privacy policies.

Every major security incident in the VPN industry involving user data exposure has involved closed-source VPN services. The open source VPN protocols (WireGuard, OpenVPN, IPsec) have had vulnerabilities discovered and fixed through the normal security research process, but none have resulted in mass user data exposure because the protocols themselves do not collect or store user data. When configured correctly, they simply encrypt and route traffic.

The United States National Institute of Standards and Technology (NIST), the European Union Agency for Cybersecurity (ENISA), and numerous other standards bodies have published guidance recommending open source software for security-critical applications, specifically citing the ability to audit code as a key security advantage. This institutional endorsement reflects the security community's consensus that transparency improves security.

How to Maximize Open Source VPN Security

To get the full security benefit of an open source VPN, choose well-established projects with active communities and published audit histories. WireGuard and OpenVPN are the safest choices for the protocol layer. If using a VPN service, choose one that publishes its client source code and has undergone independent security audits with publicly available results.

Keep your VPN software updated. Security patches are only effective if you install them. Enable automatic updates on your server and keep client applications current. For self-hosted setups, enable unattended security updates on the server operating system to ensure kernel and package vulnerabilities are patched without manual intervention.

Verify your configuration after setup. Run DNS leak tests, WebRTC leak tests, and IPv6 leak tests to confirm that all traffic routes through the tunnel as expected. Test both Wi-Fi and cellular connections if using a mobile VPN. A VPN that leaks DNS queries or IPv6 traffic provides a false sense of security that may be worse than no VPN at all.