CVE-2015-8660 in Linux
Summary
by MITRE
The ovl_setattr function in fs/overlayfs/inode.c in the Linux kernel through 4.3.3 attempts to merge distinct setattr operations, which allows local users to bypass intended access restrictions and modify the attributes of arbitrary overlay files via a crafted application.
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Analysis
by VulDB Data Team • 11/25/2024
The vulnerability identified as CVE-2015-8660 resides within the Linux kernel's overlay filesystem implementation, specifically in the ovl_setattr function located at fs/overlayfs/inode.c. This flaw affects kernel versions through 4.3.3 and represents a significant security weakness that undermines the integrity of the overlay filesystem's access control mechanisms. The overlay filesystem is designed to present multiple filesystems as a single unified filesystem, commonly used in containerization technologies and various Linux distributions to provide layered filesystem access. The vulnerability manifests when the kernel attempts to merge distinct setattr operations, creating a scenario where legitimate access restrictions are bypassed.
The technical flaw stems from improper handling of attribute modification operations within the overlay filesystem's inode management system. When an application attempts to modify file attributes through the overlay filesystem, the ovl_setattr function incorrectly processes these operations by merging them in a way that disregards the underlying filesystem's access controls. This merging behavior allows a local attacker to manipulate files that should be restricted or protected by the overlay filesystem's access policies. The vulnerability specifically enables attackers to modify the attributes of arbitrary overlay files regardless of their actual permissions or the intended access restrictions imposed by the underlying filesystem layers.
The operational impact of this vulnerability is substantial for systems utilizing overlay filesystems, particularly those running kernel versions affected by CVE-2015-8660. Local users can exploit this weakness to bypass access controls and modify files that should remain protected, potentially leading to privilege escalation or data corruption. The vulnerability is particularly concerning in containerized environments where overlay filesystems are commonly used for layer management, as it could allow attackers to modify critical container components or gain unauthorized access to sensitive data. This issue aligns with CWE-284, which addresses improper access control, and represents a classic example of how filesystem-level vulnerabilities can compromise system security through improper privilege handling.
Mitigation strategies for CVE-2015-8660 primarily focus on kernel version updates, as the vulnerability was resolved in kernel versions beyond 4.3.3. System administrators should prioritize upgrading to patched kernel versions to eliminate the risk. Additionally, organizations should implement monitoring for suspicious attribute modification activities within overlay filesystems, particularly in environments where containerization technologies are deployed. The ATT&CK framework categorizes this vulnerability under privilege escalation techniques, specifically targeting the 'File and Directory Permissions Modification' tactic. Organizations should also consider implementing additional security controls such as mandatory access controls, file integrity monitoring, and regular security audits of filesystem operations to detect and prevent exploitation attempts. The vulnerability demonstrates the importance of proper access control implementation in kernel-level filesystem operations and highlights the need for thorough testing of filesystem interaction mechanisms to prevent similar issues in other kernel subsystems.