CVE-2015-2925 in Linux
Summary
by MITRE
The prepend_path function in fs/dcache.c in the Linux kernel before 4.2.4 does not properly handle rename actions inside a bind mount, which allows local users to bypass an intended container protection mechanism by renaming a directory, related to a "double-chroot attack."
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Analysis
by VulDB Data Team • 07/17/2024
The vulnerability described in CVE-2015-2925 resides within the Linux kernel's filesystem implementation, specifically in the prepend_path function located in fs/dcache.c. This flaw represents a significant security issue that affects Linux kernel versions prior to 4.2.4, creating a path traversal vulnerability that undermines container security mechanisms. The vulnerability stems from improper handling of rename operations within bind mount contexts, which creates a critical gap in the kernel's path resolution logic that malicious users can exploit to circumvent containment policies.
The technical flaw manifests when a local attacker performs a rename operation on a directory within a bind mount structure. The prepend_path function fails to correctly account for the relationship between the original and renamed directory paths, leading to a situation where the kernel's path resolution mechanism becomes confused about the proper directory hierarchy. This confusion enables attackers to manipulate their filesystem access in ways that should have been prevented by container isolation mechanisms. The vulnerability is particularly dangerous because it operates at the kernel level, meaning that successful exploitation can bypass traditional user-space security controls and containment measures.
The operational impact of this vulnerability is severe for containerized environments where Linux kernel security features are relied upon for isolation. Attackers can leverage this flaw to perform what is known as a "double-chroot attack" where they first establish a chroot environment and then use the rename functionality to escape the intended containment boundaries. This allows malicious users to access files and directories that should be restricted within the container context, potentially leading to privilege escalation and unauthorized access to sensitive system resources. The vulnerability affects any system running vulnerable kernel versions where bind mounts and containerization technologies are in use, making it particularly relevant for cloud computing environments and container orchestration platforms.
The security implications extend beyond simple path traversal, as this vulnerability directly impacts the fundamental security model of containerization technologies that depend on kernel-level path handling for isolation. According to CWE classification, this represents a weakness in the kernel's path resolution system, specifically related to improper handling of filesystem operations within mounted filesystem contexts. The ATT&CK framework would categorize this as a privilege escalation technique that leverages kernel-level vulnerabilities to bypass containment mechanisms. Organizations using Linux containers, virtualization platforms, or any system that relies on bind mounts for security isolation should consider this vulnerability as a critical risk that could allow attackers to break out of restricted environments and access unauthorized resources. The fix for this vulnerability required modifications to the kernel's path resolution logic to properly account for rename operations within bind mount contexts, ensuring that path traversal remains consistent with the intended security boundaries established by containerization technologies.