What is a likely reason for certificate warning errors during SSL inspection when visiting HTTPS websites?

The selection of the option regarding the browser not recognizing the certificate as trusted is accurate because certificate warnings often occur when a browser encounters a certificate it cannot validate against its list of trusted certificate authorities (CAs).

In SSL inspection, an intermediary device, such as a FortiGate, acts as a man-in-the-middle between the client and the server. It inspects and decrypts the traffic, which entails presenting its own certificate to the client. If this certificate is not signed by a CA that the browser recognizes as trustworthy, the browser will issue a warning about the potential security risk. This warning is a safeguard to inform users that the connection may not be secure and that the authenticity of the certificate presented cannot be verified.

When conducting SSL inspection, it is essential that the certificate used by the intermediary (FortiGate) is properly installed on client devices and is recognized as trusted. This typically involves installing the root certificate of the inspecting device into the browser's trusted store. If this step is missed, users will encounter certificate warnings when attempting to access HTTPS websites.

The other options, while relevant to SSL issues, do not directly explain the reason behind certificate warnings as clearly as the chosen option. For example, an expired private CA certificate could indeed cause