Kirby is an open-source content management system. Prior to 4.9.4 and 5.4.4, Kirby sites and plugins using the Kirby Http Remote class, including Remote::request(), Remote::get(), and Remote::post(), to send outgoing HTTP requests with untrusted data in the headers option could allow newline characters in a header value to inject a separate unintended request header to the remote service. This issue is fixed in versions 4.9.4 and 5.4.4.

Kirby: Request header injection in `Http\Remote`