SMB User Authentication Bypass

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

Description

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

• ownCloud Server < 9.1.2 (CVE-2016-????)
  • apps/5d47e7b52646cf79edadd78ce10c754290cbb732
• ownCloud Server < 9.0.6 (CVE-2016-????)
  • apps/16cbccfc946c8711721fa684d78135ca1fb64791
• ownCloud Server < 8.2.9 (CVE-2016-????)
  • apps/a0e07b7ddd5a5fd850a6e07f8457d05b76a300b3

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.

Acknowledgements

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

• Dwight Hohnstein – Rhino Security Labs – Vulnerability discovery and disclosure.

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