CVE-2014-9278 in OpenSSH
Summary
by MITRE
The OpenSSH server, as used in Fedora and Red Hat Enterprise Linux 7 and when running in a Kerberos environment, allows remote authenticated users to log in as another user when they are listed in the .k5users file of that user, which might bypass intended authentication requirements that would force a local login.
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Analysis
by VulDB Data Team • 04/07/2022
The vulnerability identified as CVE-2014-9278 represents a critical authorization flaw in OpenSSH server implementations running within Kerberos environments on Fedora and Red Hat Enterprise Linux 7 systems. This issue stems from improper handling of Kerberos authentication mechanisms when users are listed in the .k5users file, creating an unintended privilege escalation pathway that undermines the security controls designed to enforce proper authentication procedures. The flaw specifically affects systems where OpenSSH operates in conjunction with Kerberos authentication, which is commonly deployed in enterprise environments requiring centralized authentication services. When properly configured, Kerberos should provide robust authentication guarantees, but this vulnerability creates a scenario where authenticated users can potentially impersonate other users who have been granted specific access through the .k5users file configuration.
The technical root cause of this vulnerability lies in the interaction between OpenSSH's authentication process and Kerberos user mapping mechanisms. When a user authenticates through OpenSSH in a Kerberos environment, the system checks for the presence of a .k5users file in the target user's home directory. If the authenticating user is listed in this file, the system incorrectly grants access to the target user's account without properly validating that the authenticating user possesses legitimate credentials for that specific account. This behavior violates fundamental security principles of authentication and authorization, as it allows for arbitrary user impersonation based solely on file membership rather than proper authentication validation. The vulnerability manifests when the OpenSSH server fails to enforce proper authentication boundaries between users, creating a scenario where legitimate authentication can be bypassed through manipulation of Kerberos user mapping files.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally undermines the trust model of Kerberos-authenticated systems. An authenticated user who can identify another user with a .k5users file entry can potentially access sensitive data, execute commands, and perform actions as that target user without proper authentication. This creates significant risks for enterprise environments where multiple users share systems and where proper access controls are essential for maintaining data integrity and confidentiality. The vulnerability is particularly concerning in environments where administrative privileges are granted through Kerberos mappings, as it could potentially allow attackers to gain elevated access to critical system resources. Organizations relying on Kerberos for authentication and authorization are particularly vulnerable, as the flaw operates at the authentication layer where proper access controls should be enforced.
Security mitigations for this vulnerability involve several approaches that address both immediate remediation and long-term architectural improvements. The primary solution is to apply the official patches provided by Red Hat and Fedora that correct the authentication flow in OpenSSH when operating within Kerberos environments. Administrators should also review and audit .k5users file configurations to ensure that only legitimate users have entries that could enable unauthorized access. Additionally, implementing proper monitoring and logging of authentication events can help detect suspicious access patterns that might indicate exploitation attempts. Organizations should consider implementing additional authentication controls such as two-factor authentication or role-based access controls to add layers of protection beyond the Kerberos system itself. This vulnerability aligns with CWE-284, which addresses improper access control, and represents a specific instance of privilege escalation through authentication bypass mechanisms. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and authentication bypass methods that adversaries might use to maintain persistent access within compromised environments. The flaw demonstrates the importance of proper authentication boundary enforcement and highlights the risks associated with complex authentication systems that integrate multiple security mechanisms without adequate validation controls.