The most used web security policy mechanism is HTTP Strict Transport Security (HSTS). This header protects web applications against protocol downgrade attacks and cookie hijacking. This header also restricts the application from using only HTTPS communication. The header won’t allow communications via the insecure HTTP protocol. There are many web applications with the HTTP Strict Transport Security (HSTS) header cannot be recognised. These web applications are being served from not only HTTP but also HTTPS. It also lacks proper implementation of HSTS policy. HTTP Strict Transport Security is a web security policy mechanism to interact with complying user agents such as a web browser using only secure HTTP connections. This header informs the browser that, the site should not be loaded over HTTP. This header automatically converts all the requests to the site from HTTP to HTTPS.
The following is the example of strict transport security header.
The main impact under this vulnerability:-