What Is OpenVPN? How It Works, Vulnerabilities & More

November 4, 2026 ByNancy WilliamNo Comments 7 minutes

What is OpenVPN? Most VPNs have the OpenVPN protocol; you can either set it as the default or tweak it in the VPN’s settings.  

Some set it because it looked familiar, or because it was already selected. But what actually is it? Why do so many providers still rely on a protocol that’s been around for over two decades?

The short answer is that OpenVPN is the workhorse of the VPN world. It may not be the fastest or the newest, but it’s earned a reputation for being reliable, secure, and incredibly flexible.

This guide breaks down what OpenVPN is, how it works, where it’s best used, and its cons.

What Is OpenVPN?

OpenVPN is a VPN protocol. It defines how your device talks to a VPN server. It handles the handshake, encryption, and the way your data travels through the tunnel.

OpenVPN has been around for over two decades, released in 2001 by James Yonan. It’s open-source, which means anyone can inspect its code, find bugs, and suggest fixes. That transparency is a big reason security experts trust it.

Unlike some newer protocols that run on a fixed set of rules, OpenVPN is highly configurable. You can run it over UDP for speed or TCP for reliability. 

Alternatively, you can choose from a wide range of encryption ciphers. You can even set it up on a router, a Raspberry Pi, or a server you control. That flexibility is both OpenVPN’s greatest strength and its biggest headache. We’ll get into that later on, but first, let’s talk about how OpenVPN works.

How Does OpenVPN Work?

OpenVPN creates a secure tunnel between your device and a VPN server. Here’s the simplified version of what happens when you hit “Connect.”

Step 1 – The Handshake

Your VPN client reaches out to the server. They introduce themselves and agree on how they’ll communicate. OpenVPN uses SSL/TLS, the same technology that secures HTTPS websites, to establish a trusted connection.

Step 2 – Authentication

The server checks that you are who you say you are. OpenVPN supports several methods of authentication. These include: 

• Certificates: The most robust option, often used in corporate setups.
• Username and password: Common with commercial VPN providers.
• Pre-shared keys: A simpler, less flexible option for specific setups.

Step 3 – Key Exchange

Once authenticated, your device and the server create a set of encryption keys. OpenVPN uses Perfect Forward Secrecy (PFS), which means these keys are temporary. This means that even if someone steals one key, they can’t use it to decrypt past sessions.

Lastly – The Tunnel

Your data gets encrypted, wrapped in a packet, and sent through the tunnel to the server. The server decrypts it and forwards it to the internet. It then does the same thing in reverse when the response comes back.

OpenVPN Security in 2026 – What’s Changed?

Many guides often paint a very positive picture of OpenVPN, which they should, but we’re here to tell you that there are other sides to its security. Yes, OpenVPN is secure; that’s true, but security isn’t a simple yes or no. Here’s what you need to know in 2026:

OpenVPN Has Had Recent Vulnerabilities

OpenVPN isn’t immune to bugs. In 2026 alone, security researchers disclosed several vulnerabilities:

• CVE-2026-35058: A flaw in how OpenVPN handled certain packets allowed authenticated attackers to crash the server, causing a denial of service.
• CVE-2025-15497: A similar denial-of-service issue related to key slot processing in OpenVPN 2.7 alpha and release candidates.
• CVE-2026-63650: A vulnerability that could misidentify authenticated users when using the mbedTLS library, potentially allowing impersonation.

However, these flaws do not mean OpenVPN is broken. They mean you should keep your VPN app updated, which our guides have been repeating. 

FastestVPN always ensures that these issues are patched quickly. But if you’re running an old version of OpenVPN on a self-hosted setup, check for updates.

OpenVPN’s Flexibility Can Be a Security Risk

Because OpenVPN lets you choose from many ciphers, some often configure it poorly. You could end up using an outdated cipher like Blowfish or a weak hash like SHA1 if you’re not careful.

Modern OpenVPN versions negotiate strong ciphers by default. But this is a reason to trust your VPN provider’s defaults rather than manually configuring everything yourself unless you know what you’re doing.

OpenVPN Better Anonymity Than WireGuard (Some Cases)

This is a nuance that rarely gets mentioned. A 2025 academic study compared OpenVPN and WireGuard and found that OpenVPN provides stronger anonymity in certain scenarios. 

WireGuard’s packet structure exposes receiver and counter values, which can make traffic pattern analysis easier. OpenVPN’s design makes traffic analysis patterns harder.

Why does this matter? 

Well, if you’re using a VPN to avoid traffic analysis, not just to hide your IP, OpenVPN has a subtle advantage over WireGuard.

OpenVPN vs WireGuard – Which Should You Use?

This is the comparison everyone often asks about, and here’s an honest breakdown of the two: 

Our recommendation would be to use WireGuard for everyday browsing, streaming, and gaming. You can use OpenVPN when you’re on a restrictive network, when you need TCP mode to bypass a firewall, or when you want that extra layer of traffic analysis resistance.

FastestVPN supports both, so you can switch whenever you need to.

OpenVPN TCP vs OpenVPN UDP – What’s the Difference?

OpenVPN runs in two modes, and choosing the right one matters. Here are their core differences: 

Why TCP matters: TCP mode can disguise VPN traffic as regular HTTPS traffic on port 443. If you’re on a network that blocks VPNs, TCP mode often gets through. UDP is faster, but it’s easier to block.

TIP – If your connection feels slow or unstable, try switching between TCP and UDP in the FastestVPN app settings. Sometimes one works better than the other on a specific network.

How to Set Up OpenVPN with FastestVPN

FastestVPN supports OpenVPN on all major platforms. Here’s the quick version for Windows, macOS, iOS, and Android.

Using the FastestVPN App

• Download the FastestVPN app from the official website.
• Log in with your credentials.
• Open “Settings” and find the “Protocol” option.
• Select “OpenVPN.” You can choose either UDP or TCP. See what works better for you.
• Connect to a server.
• That’s it. 

Manual Setup (For Advanced Users)

If you need to set up OpenVPN manually, on a router, a Linux machine, or a device without the FastestVPN app, FastestVPN provides configuration files and step-by-step guides.

For example, the FastestVPN support site has a guide for setting up OpenVPN on Kubuntu via the command line. You download the .ovpn files, install OpenVPN, and connect using your credentials.

For iOS, you can download the OpenVPN Connect app, import the configuration files, and enter your FastestVPN username and password.

Frequently Asked Questions

To Conclude

OpenVPN isn’t the “newest” or the fastest protocol you can use. However, it’s still one of the most reliable, secure, and incredibly flexible. Even today in 2026, it still has advantages that WireGuard doesn’t match.

So, we suggest using OpenVPN when you need to bypass a stubborn firewall. Use it when you want the extra anonymity that comes from its traffic patterns. Connect with it when you’re setting up a VPN on a router or a device that doesn’t support the latest apps.

If it’s speeds you’re after, you can easily switch to WireGuard via the app’s settings. FastestVPN gives you both.