Learn how to fix the “Peer Certificate Verification Failure” error in QNAP QVPN with OpenVPN. Our pfSense Support team is here to help you with your questions and concerns.

“Peer Certificate Verification Failure” Error in QNAP QVPN with OpenVPN

If you have run into the “Peer certificate verification failure” error when connecting OpenVPN clients to QNAP’s QVPN Service, you’re not alone.

This issue usually occurs during the SSL/TLS handshake process. The root cause is often outdated certificates or incompatibilities between QVPN and newer versions of the OpenVPN client.

Let’s break down what causes this error and how to fix it.

What Causes the “Peer Certificate Verification Failure” Error?

This error has become increasingly common, particularly with the introduction of OpenVPN Connect version 3.4.0 and above, which utilize OpenSSL 3.0.8, a version that sticks to stricter cryptographic standards.

Unfortunately, QVPN’s older certificate system doesn’t always keep up, resulting in failed connections.

This scenario is not unique to QNAP. VPN and firewall solutions, such as pfSense, have faced similar compatibility issues. For instance, version mismatches and network misconfigurations can cause problems, such as the pfSense installer daemon failing to connect, which is often tied to outdated components or mismatched versions.

Common Causes

• QVPN’s OpenVPN server may use certificates that no longer comply with the latest cryptographic standards required by OpenVPN Connect.
• OpenVPN Connect 3.4.0 and newer versions (based on OpenSSL 3.0.8) are incompatible with older QVPN certificates.
• If we are using an old `.ovpn` file, it may contain expired or invalid certificates, which can cause verification failures.
• Newer OpenVPN clients enforce higher security levels, which reject weak or unsupported server-side certificates.

It’s worth noting that misalignments like this aren’t limited to VPN settings. Even basic network interface changes can cause issues, such as the pfSense interface mismatch error, highlighting the importance of tight configuration control in any networking environment.

How to Fix the Error

The best way to resolve this issue is to update both your QVPN Service and its peer certificate, then download and import the latest configuration file into our OpenVPN client.

Step 1: Update QVPN Service

1. First, open App Center on your QNAP device.
2. Then, find QVPN Service in the list.
3. Next, click Update or Required Update if available.
4. Confirm when prompted and then wait for the latest version to install.

Step 2: Update the Peer Certificate

1. To begin with, open the QVPN Service app.
2. Then, go to VPN Server > OpenVPN.
3. Now, click Update Certificate. This option appears only if the current certificate is outdated.
4. Click Apply to proceed with the update.
5. Then, under Configuration file, click Download to get the updated `.ovpn` file.
6. Finally, import this file into the OpenVPN Connect client.

If you’re running into persistent issues even after these updates, ensure that the client security settings haven’t defaulted to high-restriction levels.

We can also use an earlier client version, OpenVPN Connect 3.3.7 or below, which is more tolerant of older cryptographic settings. A similar principle applies in environments like pfSense, where users often discover that stricter rules can cause outbound NAT rules to stop working properly until they adapt configurations to meet current security expectations.

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Conclusion

The “peer certificate verification failure” in OpenVPN when used with QNAP’s QVPN service is primarily caused by outdated certificates and compatibility issues with newer OpenVPN/OpenSSL versions.

In brief, our Support Experts demonstrated how to resolve the “Peer Certificate Verification Failure’ error in QNAP QVPN using OpenVPN.