How to Fix “VPN Certificate Validation Failure” Error
The “VPN certificate validation failure” error is exclusive to the Cisco AnyConnect VPN client for Windows, Mac, and Linux. An added reason for a quick solution is that the software is frequently used in a business setting, interconnecting computers into a secure, efficient network. And while it performs wonderfully most of the time, things sure can go wrong unexpectedly. What’s more, employees can’t always reach a network engineer and are often left to their own devices. That’s precisely when we’d like to swoop in and save the day. Let’s demonstrate how to fix the “VPN certificate validation failure” error.
1. Go through standard troubleshooting steps
Before you get into an array of unnecessary steps, make sure the problem isn’t a glitch, bug, or temporary downtime. By this, we mean going through steps 1 through 6 in our “VPN connection failed. The Request was aborted” error fix guide. Once you’ve tried that and it didn’t work, press on.
2. Double-check the VPN client profile
In essence, you need to verify the hostname and host address are still valid. Even if you haven’t made changes manually, your network admin might have, to the server or the client. To demonstrate this, we’ll use Cisco AnyConnect VPN client profile on macOS:
- Find the profile file with a .XML extension in the “/opt/cisco/anyconnect/profile” folder.
- Confirm that the bolded parts are still correct:
<ServerList>
<HostEntry>
<HostName> Hostname for VPN </HostName>
<HostAddress> FQDN (Fully Qualified Domain Name) or server’s IP address </HostAddress>
</HostEntry>
</ServerList>
3. Has the SSL/TLS certificate expired?
A common cause of the “VPN certificate validation failure” error is the expiration of the SSL certificate. While in the past they were issued for longer, in 2021 the period is reduced to either 12 months or 13 months (397 days). Although there are many ways to do this, we’ll use the ASDM client to demonstrate checking SSL/TLS certificate expiration date:
- Open the ASDM interface for your device and operating system. We’ll use Windows Cisco ASDM for ASA.
- Switch to the Configuration tab in the top left corner.
- Go to Device Management, then Certificate Management.
- Select CA Certificates.
- Click the Show Details button on the right-hand side.
- In the General tab, check the dates listed under Valid From and Valid To.
4. Install a new SSL or TLS certificate
If your certificate expired, then you know regenerating them is the way to fix the “VPN certificate validation failure” error. Here’s what to do:
- Follow steps 1 through 4 above.
- Highlight expired certificates and click on the Delete button to remove them.
- Download renewed certificates.
Tip. We’ll demonstrate this using “DigiCert CA” chain certificates: High Assurance EV Root CA and SHA2 High Assurance Server CA, available at www.digicert.com/digicert-root-certificates.htm. - After downloading, go back to the CA Certificates window and click on the Add button.
- On the Install Certificate window, click on the Install from a file button.
- Click on Browse…, select a digital certificate file, then click on Install.
- Finally, click on Install Certificate, then Send at the Preview CLI Commands prompt.
- Repeat steps 4-8 for the other certificate file.
I want to use the PEM client certificate. What should I do?
So, you’re using AnyConnect VPN on Linux or Mac. If you haven’t installed certificates yet, download the client certificate and its private key and place them here:
Clarification. The certificate must end with .pem while the private key must end with .key. Also, they must have identical file names.
5. Configure cryptography
Although there are ways to do this within the GUI, it’s much quicker and easier to simply run CLI (command-line interface) commands. Here’s what you can try:
1. Allowing SSL client certificates to be used on the outside
This is a step Cisco itself recommends as a permanent fix for the “VPN certificate validation failure” error. It simply makes client-side certificates available externally. Here’s how to proceed:
- Launch Cisco Client CLI like this:
- Windows. Go to “C:/Program Files/Cisco/Cisco AnyConnect Secure Mobility Client” then open a file named vpncli.exe.
- Mac or Linux. Visit the “/opt/cisco/anyconnect/bin/” location and open the file named vpn.
2. Fixing TLS version mismatch and changing cryptography method
There’s a chance that your VPN client isn’t up to date, or that there’s some sort of conflict which makes it use TLS 1.0 or TLS 1.1. This creates a problem when your cryptography tries to negotiate TLS 1.2. To fix this, open the CLI and proceed in one of 3 ways:
- Change cipher version by entering:
ssl cipher tlsv1.2 - Adjust TLS 1.2 cipher to use stronger cipher suites by entering this code:
ssl cipher tlsv1.2 custom “AES256-SHA:AES128-SHA:DHE-RSA-AES256-SHA:DHE-RSA-AES128-SHA:DES-CBC3-SHA:DES-CBC-SHA:RC4-SHA:RC4-MD5” - Configure the DTLS version and its cipher suites. Type the following command:
ssl cipher dtlsv1 custom “AES256-SHA:AES128-SHA:DES-CBC3-SHA”
6. Enable or disable Windows OCSP Service Nonce
Without getting into specifics, you should know that Microsoft Windows uses RFC 5019 while Cisco AnyConnect VPN’s ASA is only compliant with RFC 2560. As such, on Windows, it won’t accept requests signed by ASA certificates and thus print “VPN certificate validation failure” error. You can fix this in one of 2 ways:
1. Enable OCSP Nonce on Windows Server
Are you (or your company) using an Online Certificate Status Protocol (OCSP) responder on your Windows Server? If so, do this:
- Open your Windows Server OCSP responder client.
- Go to Administrative Tools then Online Responder Management.
- Click on the Revocation Configuration option in the left sidebar.
- Right-click on your certificate and select Edit Properties.
- In the Signing tab, put a checkmark in front of Enable NONCE extension support.
2. Disable Nonce via ASA TrustPoint
Although Cisco recommends the method above, you can also try to disable OCSP via the CLI. After launching the appropriate interface, use these commands:
- ASA(config)# crypto ca trustpoint WIN-2K12-01_Root_CA
- ASA(config-ca-trustpoint)# ocsp disable-nonce
Tip. Replace WIN-2K12-01_Root_CA with the actual TrustPoint name of your certificate (you can see it using method 4).
Milan
VPN is one of my passions. I love being secure and helping others avoid any potential threats online. I also contribute to several VPN guide websites online.
How to Fix VPN Certificate Validation Failure Error
A VPN is a service that provides you with security while online. It establishes a private connection by routing your traffic through an encrypted tunnel, hiding your IP address and internet activity from third parties and other prying eyes.
VPN usage is popular for both personal and business use, as the number of data breaches and privacy violations continue to grow. With approximately 1.2 billion internet users worldwide employing a VPN service, they have become a vital part of our online experience.
A free VPN service can allow you to enjoy greater internet freedom and bypass geo-restrictions to access content and streaming libraries from other countries. Enhanced security and unblocking content are two of the biggest reasons individuals and businesses employ a VPN.
That being said, VPN can be a very frustrating experience when you are faced with a VPN error. While VPNs can still be open to threats such as malware, a common problem with VPN clients is establishing the connection via the VPN certificate.
What is a VPN Certificate and Why Do We Need One?
The VPN client needs a VPN certificate to authenticate that you are connecting to their server. Digital certificates, much like using pre-shared keys for authentication, are another means to confirm you are who you really are.
An SSL certificate will be used by your VPN gateway to verify that it is the device it claims to be. These certificates are more secure than a pre-shared key, but they expire for security reasons or when they need to be replaced.
In 2020, Apple announced that TLS/SSL server certificates would not have a validity period greater than 397 days. This change made it vital to fix any VPN certificate validation error as soon as possible. Individuals use Virtual Private Networks to improve their security and privacy while browsing the internet.
As a result, if you are unable to validate VPN security, the purpose of obtaining the VPN in the first place becomes pointless. Although there are other types of security software out there, VPNs are an excellent tool to both protect your data and open access to more content online. Let’s look at a few common reasons for VPN certificate validation.
Common Reasons for VPN Certificate Validation Failure
There are numerous reasons why this could occur. It is possible that your device does not recognize the certificate of the VPN server as valid. There are several options for resolving this.
One approach is to add the VPN server’s certificate to the trusted certificate list on your device. Another solution is to install a third-party VPN client that enables certificate validation. If you are still experiencing issues, you should contact your VPN provider for assistance.
However, before you go through troubleshooting steps, it’s worth checking that the problem isn’t temporary downtime on the VPN client’s part, a glitch, or a bug. This can be solved by reconnecting to the VPN, restarting your router, or temporarily disabling your firewall. You should also make sure your VPN provider is compatible with your chosen network, such as Firefox.
The most common reason for a VPN certificate validation failure is an expired certificate. You can check whether your certificate is still valid in the interface of your VPN provider. Fixing this will depend on whether your certificate is externally signed for the VPN firewall or whether it is internally signed for an external component. This is because you must manually create and renew any certificates that are not signed by the default Certificate Authority (CA).
Renewing an Externally Signed Certificate:
- Create a new certificate request
- Sign the certificate with the external certificate authority
- Import the newly signed certificate
Renewing an Internally Signed Certificate:
- Create a new certificate request in the external component
- Sign the certificate with the internal certificate authority
- Export the newly signed certificate and import it to the external component
Further Troubleshooting Steps
If you continue to encounter the error after assuring it is not a bug and verifying the validity of your certificate, you can move on to the next set of troubleshooting steps.
One probable explanation is that the certificate’s Common Name (CN) does not match the domain name being requested. In this scenario, the solution is to check that the certificate’s CN reflects the domain name. Furthermore, it is critical to ensure that the certificate is issued or signed by a trusted Certificate Authority, as the certificate cannot be validated without this step.
If you are a Mac user, the most common cause is that the VPN server is not set up to use the proper certificate. Another possibility is that the certificate is not trusted by the VPN client. In this case, both a pre-shared key and a certificate can be used as authentication methods through the VPN client interface.
Conclusion
Fixing a VPN certificate validation error as soon as possible is important to ensure your VPN client is running properly. Without troubleshooting this issue, your security is compromised until the error is resolved.
An expired certificate is likely the cause behind the error, so be sure to keep your certificate up to date and issued by a trusted certificate authority. If problems persist, it would be best to contact your VPN service provider for further assistance.