image-20250303210820130

0x01

访问靶场,回显源码

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<?php

/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2020-09-04 00:12:34
# @Last Modified by:   h1xa
# @Last Modified time: 2020-09-04 00:42:26
# @email: h1xa@ctfer.com
# @link: https://ctfer.com

*/

error_reporting(0);
if(isset($_GET['c'])){
    $c = $_GET['c'];
    if(!preg_match("/flag|system|php/i", $c)){
        eval($c);
    }
    
}else{
    highlight_file(__FILE__);
}

0x02

源码审计发现,传入的参数C被过滤掉flag、system、php、i字段

尝试构造绕过

image-20250303212731388

0x03

发现同目录下有flag.php文件,构造语句打开,获得flag

image-20250303212829558