< go back to overview

SMB User Authentication Bypass

Platform: ownCloud Server

Versions: 8.2.9, 9.0.6, 9.1.2,

Date: 11/10/2016

Risk level: High

CVSS v3 Base Score: 7.4 (AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N)

CWE: Incorrect Implementation of Authentication Algorithms (CWE-303)

HackerOne report: 148151


ownCloud includes an optional and not by default enabled SMB authentication component that allows to authenticate users against an SMB server. This backend is implemented in a way that it tries to connect to a SMB server and if that succeeded consider the user logged-in. The backend did not properly take into account SMB servers that any kind of anonymous auth configured. This is the default on SMB servers nowadays and allows an unauthenticated attacker to gain access to an account without valid credentials.

Note: The SMB backend is disabled by default and requires manual configuration in the ownCloud config file. If you have not configured the SMB backend then you’re not affected by this vulnerability.

Affected Software

Action Taken

The SMB backend is now performing an additional authentication attempt with invalid credentials. If that succeeds as well it assumes that anonymous authentications are enabled and denies the login attempt.


The ownCloud team thanks the following people for their research and responsible disclosure of the above advisory:

This advisory is licensed CC BY-SA 4.0. Original source: nextcloud.com

Share this

By continuing to use the site, you agree to the use of cookies. more information

The cookie settings on this website are set to "allow cookies" to give you the best browsing experience possible. If you continue to use this website without changing your cookie settings or you click "Accept" below then you are consenting to this.