Inconsistent handling of invalid headers causes unexpected behavior

Description

The following code:

<?php
header( "X-Foo;: hello" );
header( "X-Foo\t: hello" );
header( "X-Foo\n: hello" );

The 3rd one results in a warning (Header may not contain more than a single header, new line detected) and the header is not set.
The other 2 however are sent without a warning. The 2nd one will get fixed by nginx, however the 1st one passes through (see https://github.com/nginx/nginx/issues/899)

This not only is inconsistent, this also allows for certain attack vectors if the request is proxied and the proxy does not handle the invalid headers correctly (sorry, can't go into detail on this at this moment in time, due to pending security reports)

Since headers are apparently getting validated in PHP already (otherwise we wouldn't have an error for the 3rd one), this validation should be fixed to strictly check if the provided header adheres to the HTTP header standards

PHP Version

PHP 8.4, however affects previous PHP versions similarly

Operating System

No response

Beginne damit, die drei in der Issue beschriebenen header()-Aufrufe zu reproduzieren, und untersuche den Validierungspfad von PHP für Header darauf, wie Semikolons, Tabulatoren und Zeilenumbrüche behandelt werden. Die Arbeit ist abgeschlossen, wenn ungültige Header-Syntax konsistent mit einer geeigneten Warnung abgewiesen wird und gültige Header unbeeinträchtigt bleiben; füge Tests für die drei Beispiele hinzu.