CVE-2015-1328 in Linux
Summary
by MITRE
The overlayfs implementation in the linux (aka Linux kernel) package before 3.19.0-21.21 in Ubuntu through 15.04 does not properly check permissions for file creation in the upper filesystem directory, which allows local users to obtain root access by leveraging a configuration in which overlayfs is permitted in an arbitrary mount namespace.
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Analysis
by VulDB Data Team • 11/30/2024
The vulnerability described in CVE-2015-1328 represents a critical privilege escalation flaw within the Linux kernel's overlay filesystem implementation. This issue specifically affects Ubuntu versions through 15.04 where the kernel version is below 3.19.0-21.21, creating a significant security gap that can be exploited by local attackers to gain root-level access to affected systems. The vulnerability stems from improper permission checking mechanisms within the overlayfs subsystem, which is designed to provide a unified view of multiple filesystems by overlaying them on top of each other.
The technical flaw manifests in the overlayfs implementation's failure to properly validate file creation permissions when operating in the upper filesystem directory. This occurs specifically when overlayfs is enabled within arbitrary mount namespaces, creating a scenario where a local user can manipulate the filesystem hierarchy to bypass normal permission controls. The vulnerability exploits the fundamental trust model of the overlay filesystem, where the system assumes that operations within the upper layer directory are properly authorized, but this assumption fails when the overlayfs is configured in certain mount namespace scenarios.
From an operational perspective, this vulnerability presents a severe risk to system security as it allows local users to escalate their privileges to root level without requiring any special authentication or external attack vectors. The exploit requires only local access to the system and knowledge of the specific configuration that enables overlayfs in mount namespaces, making it particularly dangerous in environments where users might have limited access but still need to perform legitimate administrative tasks. The impact extends beyond simple privilege escalation, as root access provides complete control over the affected system including the ability to modify system files, install malicious software, and potentially compromise network communications.
The vulnerability aligns with CWE-276, which addresses improper permission assignment, and maps to ATT&CK technique T1068, which covers privilege escalation through local exploitation. Organizations should implement immediate mitigations including updating to kernel versions 3.19.0-21.21 or later, disabling overlayfs functionality when not required, and carefully reviewing mount namespace configurations that might enable this vulnerability. Additionally, system administrators should consider implementing additional security controls such as mandatory access controls or enhanced logging to detect potential exploitation attempts. The fix requires kernel-level patches that properly enforce permission checks during overlayfs operations, ensuring that file creation in the upper filesystem directory properly validates user permissions before granting access.