CVE-2014-4014 in Linux
Summary
by MITRE
The capabilities implementation in the Linux kernel before 3.14.8 does not properly consider that namespaces are inapplicable to inodes, which allows local users to bypass intended chmod restrictions by first creating a user namespace, as demonstrated by setting the setgid bit on a file with group ownership of root.
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Analysis
by VulDB Data Team • 11/25/2024
The vulnerability described in CVE-2014-4014 represents a critical capability implementation flaw within the Linux kernel that affects versions prior to 3.14.8. This issue stems from the improper handling of user namespaces in conjunction with file capabilities and permission models, creating a significant bypass mechanism for local attackers. The flaw specifically targets the kernel's capabilities subsystem which is designed to provide fine-grained privilege control beyond traditional user and group permissions. When a user creates a new user namespace, the kernel's capability checking mechanism fails to properly account for the fact that certain namespace operations should not apply to inodes in the same way they do to processes, leading to unexpected behavior in permission enforcement.
The technical execution of this vulnerability involves leveraging user namespace creation to manipulate file permissions in ways that should otherwise be restricted. An attacker can create a new user namespace and then modify file capabilities, particularly the setgid bit, on files that are owned by the root group. This bypass occurs because the kernel's capability checking logic does not properly validate that the namespace context is appropriate for inode operations, allowing a user with minimal privileges to effectively escalate their permissions. The flaw operates at the intersection of Linux security mechanisms including user namespaces, file capabilities, and the traditional Unix permission model, creating a complex attack vector that exploits the inherent assumptions about namespace isolation.
From an operational impact perspective, this vulnerability enables local users to circumvent mandatory access controls and privilege separation mechanisms that are fundamental to Linux security architecture. The ability to set the setgid bit on root-owned files means that attackers can potentially gain elevated privileges or access to sensitive system resources that should be restricted to root or specific administrative users. This represents a significant compromise to the principle of least privilege and can lead to further escalation opportunities, as the attacker can now execute programs with elevated group privileges. The vulnerability is particularly dangerous because it operates within the kernel itself, meaning that any successful exploitation can potentially lead to complete system compromise depending on the target files and their associated capabilities.
The mitigation strategy for CVE-2014-4014 requires immediate kernel updates to versions 3.14.8 or later where the vulnerability has been patched. System administrators should prioritize patching all affected systems and verify that the updated kernel properly implements namespace isolation for file capabilities. Additional defensive measures include monitoring for unauthorized user namespace creation and implementing strict controls on user namespace permissions. Organizations should also review their file capability configurations and ensure that unnecessary setuid/setgid bits are removed from system files. This vulnerability aligns with CWE-276, which addresses improper privilege management, and can be mapped to ATT&CK technique T1068, which covers privilege escalation through local exploits. The patch addresses the core issue by ensuring that namespace context is properly considered when evaluating file capabilities, preventing the bypass of chmod restrictions that should prevent non-root users from setting privileged bits on root-owned files.