NextCloud / OwnCloud Cross Site Scripting

`==================================================================  
Nextcloud/Owncloud - Reflected Cross Site Scripting in error pages  
==================================================================  
  
Information  
------------------------------------------------------------------  
Name: Nextcloud/Owncloud - Reflected Cross Site Scripting in error pages  
Affected Versions: Nextcloud Server < 11.0.3  
Nextcloud Server < 10.0.5  
Nextcloud Server < 9.0.58  
Owncloud <= 9.1.5  
Vendor Homepage : https://nextcloud.com/  
https://owncloud.org/  
Vulnerability Type: Reflected Cross Site Scripting  
Severity: Low  
CVE: CVE-2017-0891  
  
  
Product  
-------------------  
  
Nextcloud is a open source software for cloud storage service. Also,  
this software are more features for synchronizing. e.g. Calendar,  
contacts, tasks or RSS readers.  
It is a fork from Owncloud. Currently, Owncloud is working on  
backporting this vulnerability to be fixed in the next release, I  
hope.   
  
  
  
  
  
Description   
  
-------------------   
  
A HTML injection vulnerability flaw in the Nextcloud and Owncloud.  
Through this vulnerability an attacker could manipulate the website.  
This vulnerability could affect to the logged users. An attacker could  
send a malicious link (that contains the manipulated URL) to a  
legitimate user that he is logged in and simulate the login screen to  
stole the password (phishing), or multiple attacks more, like XSS.  
Nextcloud and ownCloud use Content-Security-Policy which prevents  
execution of inline JavaScript. However, as of now prominently Internet  
Explorer hasn't implemented Content-Security-Policy thus being at risk  
against this reflected Cross-Site Scripting  
  
Exist more options to attack, for example, redirect the content of an  
<object> or <script> to a saved and shared items of your directory.  
Also, the mimetypes are well configured and the most browsers will not  
execute a javascript file that doesn't have the javascript content-type.  
  
  
  
Source  
code:   
  
https://github.com/nextcloud/server/pull/4228  
https://github.com/owncloud/core/pull/27723   
  
  
  
  
  
Proof of  
Concept   
  
-------------------  
PoC:  
https://site/index.php/apps/files/ajax/download.php?files=%00&dir=HTMLCODE  
  
  
  
  
Solution  
-------------------  
Update to the latest versions.  
  
  
More info:  
https://nextcloud.com/security/advisory/?id=nc-sa-2017-008  
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-0891  
https://hackerone.com/reports/216812  
  
  
  
  
Advisory Timeline  
--------------------  
  
22/03/2017 - Informed to Owncloud about the issue via Hackerone.  
28/03/2017 - Informed to Nextcloud about the issue via Hackerone.  
28/03/2017 - Nextcloud answered me and confirmed the vulnerability.  
20/04/2017 - Send an email to Owncloud security...  
21/04/2017 - Owncloud confirmed the vulnerability via HackerOne and they  
are working on the fix.  
21/04/2017 - Nextcloud awarded me with 450$!  
24/04/2017 - Nextcloud released new versions with the vulnerabilty fixed.  
08/05/2017 - Nextcloud released the security advisories.  
15/05/2017 - Public disclosure.  
  
  
  
Both are very good software. The vulnerability is not very risky. I  
guess Owncloud will release a new version this month. :)  
  
  
Credits & Authors  
--------------------  
Manuel Mancera (@sinkmanu)  
  
  
Thanks to Lukas Reschke from Nextcloud for the fast replies and  
commitment with the security. A good transparency and collaboration  
makes the software better.  
  
  
Disclaimer  
-------------------  
All information is provided without warranty. The intent is to provide  
information to secure infrastructure and/or systems, not to be able to  
attack or damage.  
`