Description:
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I'm not sure whether this is a bug in the web server or in PHP itself, but trying to access $_SERVER when PHP has received an invalid request such as:

GET www.example.com:80 HTTP/1.1

Makes the built-in web server segfault.

Test script:
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1. Create a test.php file containing this line:

<?php print_r($_SERVER);

2. Start the built-in web server on this file:

php -S localhost:8888 test.php

3. Run this PHP code to send an invalid HTTP request:

$fp = fsockopen('localhost', 8888);
fwrite($fp, "GET www.example.com:80 HTTP/1.1\r\n\r\n");
while (! feof($fp)) echo fread($fp, 1024);
fclose($fp);

The web server will segfault.