CVE-2016-9463 in ownCloud Server
Summary
by MITRE
Nextcloud Server before 9.0.54 and 10.0.1 & ownCloud Server before 9.1.2, 9.0.6, and 8.2.9 suffer from SMB User Authentication Bypass. Nextcloud/ownCloud include an optional and not by default enabled SMB authentication component that allows authenticating users against an SMB server. This backend is implemented in a way that 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 have 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 Nextcloud/ownCloud config file. If you have not configured the SMB backend then you're not affected by this vulnerability.
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Analysis
by VulDB Data Team • 11/22/2022
The vulnerability described in CVE-2016-9463 represents a critical authentication bypass flaw affecting Nextcloud and ownCloud server installations prior to specific patch versions. This vulnerability specifically targets the SMB authentication backend component that allows users to authenticate against SMB servers through a network file sharing protocol. The flaw exists in the implementation logic where the authentication system fails to properly validate the authentication method used by the SMB server during the connection process. When an SMB server is configured to accept anonymous authentication, the Nextcloud/ownCloud system incorrectly treats any successful connection as valid user authentication, regardless of whether proper credentials were provided. This misconfiguration creates a fundamental security gap in the authentication process where unauthorized access becomes possible without valid user credentials.
The technical implementation of this vulnerability stems from insufficient validation of SMB server authentication modes within the authentication backend. The system's design assumes that any successful SMB connection indicates valid user authentication, but fails to distinguish between authenticated and anonymous connections. This behavior directly violates security principles outlined in CWE-287, which addresses improper authentication issues where systems fail to properly verify user credentials. The vulnerability is particularly concerning because it leverages the default configuration settings of modern SMB servers, which typically enable anonymous access for convenience and compatibility reasons. Attackers can exploit this by configuring an SMB server with anonymous authentication enabled and then attempting to authenticate through the Nextcloud/ownCloud system, gaining unauthorized access to user accounts that would normally require proper credentials.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it represents a significant weakening of the authentication infrastructure that could lead to data breaches, privilege escalation, and unauthorized system access. An unauthenticated attacker who can reach the Nextcloud/ownCloud system and configure an SMB backend with anonymous authentication capabilities can effectively bypass the entire authentication process for any user account. This vulnerability directly maps to ATT&CK technique T1078 which covers valid accounts and legitimate credentials for unauthorized access. The risk is particularly elevated in environments where administrators may have enabled the SMB backend for legitimate purposes but failed to properly secure the underlying SMB server configuration. The fact that the backend is disabled by default provides some protection, but the vulnerability remains exploitable in configurations where it has been manually enabled and improperly secured.
Mitigation strategies for CVE-2016-9463 require both immediate patching and careful configuration management. Organizations should immediately upgrade to Nextcloud 9.0.54 or later, 10.0.1 or later, and ownCloud 9.1.2, 9.0.6, or 8.2.9 to receive the patched authentication validation logic. Additionally, administrators should conduct thorough configuration reviews to ensure that the SMB authentication backend is not enabled unless absolutely necessary for specific use cases. When the SMB backend is required, it must be configured with proper security controls including disabling anonymous authentication on the target SMB servers and implementing strict network access controls. The vulnerability highlights the importance of principle of least privilege in authentication system design and reinforces the need for comprehensive security reviews of authentication backends. Network segmentation and monitoring should be implemented to detect unauthorized configuration changes or access attempts to systems with enabled SMB authentication components, as this vulnerability can be exploited from both internal and external network positions.