HFCTF-2021-Final-easyflask

考点：

环境变量信息泄露

pickle 反序列化RCE

Flask_seesion 伪造

__ruduce__魔术方法利用

思路：

反序列化肯定包含 创建新对象的操作，如果__reduce__里包含攻击代码就可以实现RCE，但是被反序列化的输出储存在session里，需要知道密钥进行伪造。

密钥获得途径：一般都可以在 代码里、配置文件里(app.config)、环境变量里（/proc/self/environ）获得。这题属于第三者。

 首先拿到secret_key=glzjin22948575858jfjfjufirijidjitg3uiiuuhOLDPWD

/app/source源码信息:

#!/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)

因为需要伪造 session  但是我在kali 用 flask-session-cookie-manager  加密后的session 没有 反弹shell 成功。 在 window 用的脚本 也没成功。

看到别的师傅用这个脚本，试一下：

""" 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='',
                                help='Secret key', required=True)
    parser_encode.add_argument('-t', '--cookie-structure', metavar='',
                                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='',
                                help='Secret key', required=False)
    parser_decode.add_argument('-c', '--cookie-value', metavar='',
                                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))

同样是在linux 下使用

连上了之后就再也连不上了。 不搞了 这题真的浪费时间