Jenkins REST APIs vulnerable to clickjacking

Jenkins 2.218 and earlier, LTS 2.204.1 and earlier does not serve the X-Frame-Options: deny HTTP header on REST API responses to protect against clickjacking attacks. An attacker could exploit this by routing the victim through a specially crafted web page that embeds a REST API endpoint in an iframe and tricking the user into performing an action which would allow for the attacker to learn the content of that REST API endpoint.

Jenkins 2.219, LTS 2.204.2 now adds the X-Frame-Options: deny HTTP header to REST API responses, which prevents these types of clickjacking attacks.