CVE-2014-5045 in Linux
Summary
by MITRE
The mountpoint_last function in fs/namei.c in the Linux kernel before 3.15.8 does not properly maintain a certain reference count during attempts to use the umount system call in conjunction with a symlink, which allows local users to cause a denial of service (memory consumption or use-after-free) or possibly have unspecified other impact via the umount program.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 02/09/2022
The vulnerability identified as CVE-2014-5045 resides in the Linux kernel's filesystem subsystem, specifically within the mountpoint_last function located in fs/namei.c. This flaw represents a critical reference counting issue that affects kernel versions prior to 3.15.8, creating a pathway for local attackers to exploit memory management inconsistencies during umount operations involving symbolic links. The vulnerability manifests when the kernel attempts to properly handle reference counts during filesystem unmounting processes, particularly when symbolic links are involved in the mount structure.
The technical exploitation of this vulnerability stems from improper reference count maintenance during umount system calls, where the kernel fails to correctly account for mount point references when processing symbolic links. When a local user executes the umount command against a filesystem that contains symbolic links pointing to mount points, the kernel's mountpoint_last function does not properly decrement or increment reference counters, leading to potential memory corruption scenarios. This improper handling can result in either memory exhaustion through continued reference count inflation or use-after-free conditions where freed memory regions are accessed, potentially leading to system instability or arbitrary code execution.
From an operational impact perspective, this vulnerability presents a significant risk to system availability and integrity, as local users can trigger denial of service conditions that may consume system resources or cause kernel memory corruption. The use-after-free condition specifically aligns with CWE-416, which describes the reuse of memory after it has been freed, while the memory consumption aspect relates to CWE-770, representing excessive resource consumption. The vulnerability's impact extends beyond simple denial of service, as the potential for arbitrary code execution through memory corruption makes it particularly dangerous in multi-user environments where privilege escalation might be possible.
The attack vector for this vulnerability is limited to local users who have access to the system and can execute the umount command, making it a privilege escalation risk rather than a remote attack vector. However, the implications are severe given that the exploit requires only basic user privileges and can be executed repeatedly to cause sustained resource exhaustion or system crashes. Security practitioners should note that this vulnerability aligns with ATT&CK technique T1068, which describes local privilege escalation through kernel vulnerabilities, and T1499, representing network denial of service through system resource exhaustion.
Mitigation strategies for CVE-2014-5045 primarily involve upgrading to Linux kernel versions 3.15.8 or later, where the reference counting logic has been corrected to properly maintain mount point references during umount operations. System administrators should prioritize patching affected systems, particularly those running kernel versions between 2.6.39 and 3.15.7, as these versions are vulnerable to the improper reference count handling. Additionally, monitoring for unusual umount operations and memory consumption patterns can help detect potential exploitation attempts, while implementing proper access controls to limit local user privileges where possible provides an additional layer of defense against potential abuse of this vulnerability.