CVE-2014-2038 in Linux
Summary
by MITRE
The nfs_can_extend_write function in fs/nfs/write.c in the Linux kernel before 3.13.3 relies on a write delegation to extend a write operation without a certain up-to-date verification, which allows local users to obtain sensitive information from kernel memory in opportunistic circumstances by writing to a file in an NFS filesystem and then reading the same file.
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Analysis
by VulDB Data Team • 04/12/2025
The vulnerability described in CVE-2014-2038 resides within the Linux kernel's Network File System implementation, specifically in the nfs_can_extend_write function located in fs/nfs/write.c. This flaw represents a classic case of information disclosure through improper memory handling during file operations. The vulnerability affects Linux kernel versions prior to 3.13.3, making it a significant concern for systems running older kernel versions. The issue stems from insufficient verification mechanisms when handling write delegations in NFS filesystem operations, creating a window where kernel memory contents could be inadvertently exposed to local users.
The technical root cause of this vulnerability lies in the improper handling of write delegation mechanisms within the NFS subsystem. When a client performs write operations on NFS-mounted filesystems, the kernel typically relies on write delegations to optimize performance by allowing clients to cache write operations locally. However, the nfs_can_extend_write function fails to properly validate whether the write delegation remains current and valid before extending write operations. This validation gap occurs because the function does not perform adequate up-to-date verification of the delegation state, leaving room for exploitation.
The operational impact of this vulnerability manifests when local users exploit the race condition inherent in the delegation validation process. An attacker can write to a file on an NFS filesystem and then immediately read the same file, potentially capturing sensitive kernel memory contents in the process. This information disclosure occurs opportunistically, meaning the vulnerability's exploitation depends on specific timing and system conditions. The memory contents that may be exposed could include kernel data structures, credentials, or other sensitive information that should remain protected within kernel space. This type of vulnerability aligns with CWE-200, which addresses information exposure, and represents a privilege escalation vector that can be leveraged for further attacks.
The exploitation of this vulnerability demonstrates a fundamental flaw in the kernel's memory management and delegation handling protocols. Attackers can potentially extract information that may aid in more sophisticated attacks, including credential harvesting or system state reconnaissance. The vulnerability's impact is particularly concerning because it affects the kernel's core filesystem operations and can be exploited by local users without requiring special privileges beyond normal file access. This makes it a significant concern for enterprise environments where multiple users share systems and NFS filesystems are commonly used for file sharing and storage. The vulnerability's classification under ATT&CK technique T1005 (Data from Local System) highlights its potential for data exfiltration and system reconnaissance activities.
Mitigation strategies for CVE-2014-2038 primarily involve upgrading to Linux kernel versions 3.13.3 or later, where the vulnerability has been addressed through improved delegation validation mechanisms. System administrators should prioritize kernel updates and maintain current security patches to protect against this and similar vulnerabilities. Additionally, organizations can implement monitoring solutions to detect unusual NFS activity patterns that might indicate exploitation attempts. The fix implemented in kernel 3.13.3 improved the verification process for write delegations and ensured that proper up-to-date checks are performed before extending write operations, thereby eliminating the information disclosure window that existed in earlier versions.