CVE-2014-9710 in Linux
Summary
by MITRE
The Btrfs implementation in the Linux kernel before 3.19 does not ensure that the visible xattr state is consistent with a requested replacement, which allows local users to bypass intended ACL settings and gain privileges via standard filesystem operations (1) during an xattr-replacement time window, related to a race condition, or (2) after an xattr-replacement attempt that fails because the data does not fit.
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Analysis
by VulDB Data Team • 07/17/2024
The vulnerability identified as CVE-2014-9710 represents a critical race condition flaw within the Btrfs filesystem implementation of the Linux kernel prior to version 3.19. This issue specifically targets the handling of extended attributes or xattrs within the Btrfs filesystem, which are metadata elements that provide additional information about files and directories beyond standard filesystem attributes. The flaw manifests when the kernel fails to maintain consistent visibility of xattr states during replacement operations, creating exploitable time windows where malicious users can manipulate filesystem permissions and access controls. The vulnerability stems from inadequate synchronization mechanisms that allow concurrent access to xattr data structures during modification operations, enabling attackers to observe inconsistent states that could be leveraged for privilege escalation.
The technical exploitation of this vulnerability occurs through carefully timed filesystem operations that take advantage of the race condition inherent in the xattr replacement process. During the window between when an xattr replacement operation begins and when it completes, the filesystem may present inconsistent state information to different processes or threads accessing the same metadata. This inconsistency can be exploited by local users to bypass Access Control List (ACL) restrictions that should normally prevent unauthorized access to filesystem resources. The vulnerability is particularly dangerous because it operates at the kernel level within the filesystem implementation, allowing attackers to manipulate the underlying permission model without requiring external tools or elevated privileges beyond what is already available to the local user. According to CWE classification, this represents a race condition vulnerability (CWE-362) that falls under the broader category of improper locking mechanisms in concurrent systems.
The operational impact of CVE-2014-9710 extends beyond simple privilege escalation to potentially enable full system compromise when combined with other exploitation techniques. Local attackers can leverage this vulnerability to modify file permissions, access restricted resources, and potentially establish persistent access to system files and directories that should be protected by ACL settings. The race condition nature means that successful exploitation does not require specific timing or conditions but rather takes advantage of the inherent timing gaps in the filesystem's xattr handling. This vulnerability affects any Linux system running kernel versions prior to 3.19 that utilize Btrfs filesystems, making it particularly concerning for enterprise environments where Btrfs is actively deployed. The flaw can be exploited through standard filesystem operations such as file creation, modification, and attribute manipulation, making it difficult to detect and prevent through conventional monitoring approaches. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques (T1068) and potentially to persistence mechanisms (T1078) when combined with other exploitation vectors.
Mitigation strategies for CVE-2014-9710 center on immediate kernel version upgrades to 3.19 or later, which contain the necessary fixes for the xattr race condition. System administrators should prioritize patching affected systems and verify that all Btrfs filesystems are properly updated to prevent exploitation. Additionally, implementing proper filesystem access controls and monitoring for unusual xattr operations can help detect potential exploitation attempts. Organizations should also consider disabling Btrfs filesystems if they are not actively required, as this eliminates the attack surface entirely. The fix implemented in kernel version 3.19 addresses the core synchronization issues by ensuring that xattr state changes are properly atomic and visible to all processes accessing the same filesystem metadata. Regular security audits of kernel versions and filesystem configurations should be conducted to prevent similar vulnerabilities from remaining unpatched. The vulnerability serves as a reminder of the critical importance of proper concurrency control in kernel-level filesystem implementations and demonstrates how seemingly minor synchronization flaws can result in significant security implications.