What does Error self-signed certificate in certificate chain mean?

Answered by Edward Huber

Error: Self-signed certificate in certificate chain

When OpenSSL displays the error message “self-signed certificate in certificate chain”, it means that the certificate being used is self-signed and not trusted by default. This warning is important because it alerts us to a potential security vulnerability.

To understand this error better, let’s delve into the concept of certificates and certificate chains. In the context of secure communication over the internet, certificates are used to establish trust between a server and a client. They provide a way to verify the authenticity of a website and ensure that the communication between the client and server is encrypted.

Certificates are issued by certificate authorities (CAs) who are responsible for verifying the identity of the server or organization requesting the certificate. When a client connects to a server, it checks the server’s certificate to ensure that it is issued by a trusted CA. If the CA is trusted, the client can be reasonably confident that the server is who it claims to be.

In the case of a self-signed certificate, the server generates its own certificate instead of obtaining one from a trusted CA. This means that there is no external entity vouching for the server’s identity. As a result, the client cannot automatically trust the server’s certificate since it hasn’t been verified by a trusted authority.

When OpenSSL encounters a self-signed certificate in the certificate chain, it raises a warning to bring attention to the potential security risk. This warning is important because it could indicate that the server’s certificate has been tampered with or that there is a man-in-the-middle attack in progress.

A man-in-the-middle attack occurs when an attacker intercepts the communication between a client and a server, posing as the server to the client and as the client to the server. If the client blindly trusts the self-signed certificate, it could unwittingly establish a connection with the attacker instead of the intended server. This allows the attacker to eavesdrop on or manipulate the communication between the client and server.

To mitigate this risk, it is crucial to properly validate the server’s certificate. There are a few options available to handle this self-signed certificate error:

1. Trust the self-signed certificate: While not recommended in most cases, you can choose to trust the self-signed certificate if you are confident in the server’s identity. This can be done by manually adding the server’s certificate to your trust store. However, this approach should only be taken if you have verified the authenticity of the certificate through other means, such as contacting the server administrator directly.

2. Obtain a certificate from a trusted CA: The ideal solution is to obtain a certificate from a trusted CA. This involves going through a verification process where the CA confirms the identity of the server or organization. Once issued, the client will trust the certificate automatically, eliminating the self-signed certificate error.

3. Use a self-signed certificate for testing or internal purposes only: Self-signed certificates are often used in development or testing environments where the certificate’s authenticity is not critical. However, it is important to ensure that these certificates are not used in production environments where security is paramount. In such scenarios, you can instruct the client to ignore the self-signed certificate error for testing purposes, but caution should be exercised.

In my personal experience, I have encountered situations where self-signed certificates were used for internal testing purposes. While it can be tempting to ignore the warning and proceed with the connection, it is crucial to evaluate the potential risks and make an informed decision. It is always advisable to obtain proper certificates from trusted CAs to ensure secure and authenticated communication.

The error “self-signed certificate in certificate chain” indicates that the server’s certificate is self-signed and not trusted by default. This warning alerts us to the potential security risk of connecting to a server with an unverified identity. It is important to carefully evaluate the situation and take appropriate measures to ensure secure and authenticated communication.