[ACTF2020 新生赛]BackupFile

[ACTF2020 新生赛]BackupFile

wp

提示找到备份文件，找到index.php.bak

<?php
include_once "flag.php";

if(isset($_GET['key'])) {
    $key = $_GET['key'];
    if(!is_numeric($key)) {
        exit("Just num!");
    }
    $key = intval($key);
    $str = "123ffwsfwefwf24r2f32ir23jrw923rskfjwtsw54w3";
    if($key == $str) {
        echo $flag;
    }
}
else {
    echo "Try to find out source file!";
}

key是数字，然后使用intval()获取key的十进制值，与str弱相等

GET ?key=123