TLS Errors: How to Manage TLS Warnings

The Transport Layer Security (TLS) protocol is today’s most prevalent encryption protocol on the web. Websites are widely using it to establish secure connections with users. In addition, the protocol allows the safe transfer of security content, most commonly between a web server and a user’s browser.

Often, you may get different SSL/TLS warnings that indicate a TLS protocol authentication issue. An alert message from the SSL/TLS scanner doesn’t necessarily mean a direct vulnerability but highlights a potential problem that needs to be reviewed manually.

TLS Warning Security Assessment

Security Assessment Manage TLS Warning

What is a TLS Warning?

A TLS warning is a message that indicates an issue with the encryption of data transferred between a website and a client.

Such warnings are essential for several reasons, indicating a possible security issue and other problems. In particular, the proper functioning of SSL/TLS certificates is an important indicator for search engines that a website is safe to access and can be ranked high in search results.

Prevention Guide for SSL/TLS Vulnerabilities

Prevention Guide

Learn how to detect and prevent different kinds of SSL/TLS vulnerabilities.


TLS Error Types

Here are some common TLS errors, such as the prevalent TLS handshake error.

TLS/SSL Handshake Failed

The authentication process known as SSL/TLS handshake starts when a browser requests the web server to set up a secure connection. The browser then forwards a public key to the user’s computer that gets verified with the list of Certificate Authorities (CAs). Once having received the server certificate, the computer generates a key that encrypts the public one. That’s why the handshake process is an essential one for the use of SSL/TLS protocols.

The warning for ‘TLS connection failed’ is associated with a handshake fail, which is a fatal error in the authentication. The ‘TLS/SSL handshake failed’ error (also known as SSL handshake failed error and SSL handshake failed) is due to the inability to authenticate the web server. This makes the connection of the browser to this server not secure.

In essence, the issue is a matter of a mismatch between protocols or the cipher suite selection. The browser client and the web server do not have an agreement over the same SSL/TLS version.

Among the most common reasons for a TLS/SSL handshake failure are:

  • The incorrect system time on the user’s computer
  • The user’s browser configuration is incorrect
  • A Man-in-the-Middle attack is intercepting the connection
  • There is a protocol mismatch, and the web server doesn’t support the client’s protocol (compatibility issues)
  • There is a cipher suites mismatch, and the server doesn’t support the client’s cipher suites (compatibility issues)
  • The SNI-enabled servers can’t establish communication with the user’s client
  • The SSL/TLS Certificate is incorrect (the name doesn’t match the URL; the certificate chain is incomplete, or the certificate is not active)

Client TLS Negotiation Errors

Client TLS negotiation errors occur when a session with the load balancer cannot be established. The reason is usually that the client is attempting to connect to a load balancer whose security policy does not allow using the client’s protocols or ciphers.

Troubleshooting such cases ensures that the client supports at least one cipher preferred by the load balancer or a protocol set in the balancer’s security policy.

How to Fix TLS/SSL Alerts

You can consult our guide on How to Enable Secure Cookies for cookie-related issues.

If you have issues with headers, multiple overlapping headers may be present. As a consequence, the browser may choose to ignore some of the presented information. To solve the issue, ensure that the sent headers don’t overlap and don’t contain contradicting information. For more information on Security Headers, you can refer to our guide on How to Enable Security Headers for security parameters.

For all TLS/SSL alerts, it’s crucial to install the most up-to-date security updates.

For a complete overview of your digital assets’ security, Crashtest Security is here to help. Our powerful security tool, the Vulnerability Testing Software, allows you to conduct in-depth analyses of safety issues — including the CRIME attack, FREAK attack, BEAST attack, and many more — so you can ensure 360-degree protection of your systems from any attack scenario.


What is a TLS connection?

Transport Layer Security (TLS) is today’s most commonly used encryption protocol. It is used across the internet to provide security for data transfers and communication. Establishing a TLS connection entails setting a connection over a TLS protocol.

How secure is TLS?

TLS is deemed to be the current industry standard for internet security protocols. Its predecessor is the Secure Socket Layers (SSL), but today it’s not considered safe enough. Nevertheless, TLS is the most widely used protocol version on the web by major browsers.

What is a TLS error?

TLS errors occur when there are obstacles to establishing a security exchange communication between a client and a web server. The most common error is the TLS/SSL handshake failure.

What happens in case of the error ‘TLS/SSL handshake failed’?

When there is a handshake fail, the secure connection between the web server and the user’s client is not set up. Unfortunately, the TLS protocol cannot provide the necessary level of secure encryption, so communications security is not guaranteed.

How to fix TLS errors?

The reasons for receiving TLS warnings for errors can be different. They can be either on the client or server side. This means that the resolution of the mistakes is other in each particular case. However, there are still some common issues to watch out for, such as wrong system time and browser configuration on the user’s side. Fixing protocol or cipher suite mismatches on the server side often solves the errors.

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