CVE-2014-9717 in Linux
Summary
by MITRE
fs/namespace.c in the Linux kernel before 4.0.2 processes MNT_DETACH umount2 system calls without verifying that the MNT_LOCKED flag is unset, which allows local users to bypass intended access restrictions and navigate to filesystem locations beneath a mount by calling umount2 within a user namespace.
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Analysis
by VulDB Data Team • 07/27/2022
The vulnerability described in CVE-2014-9717 represents a critical privilege escalation flaw in the Linux kernel's mount management subsystem. This issue exists in the fs/namespace.c file and affects all Linux kernel versions prior to 4.0.2, creating a persistent security weakness that has remained unpatched for several years. The vulnerability specifically targets the umount2 system call implementation, where the kernel fails to validate the MNT_LOCKED flag during MNT_DETACH operations, allowing malicious actors to exploit this oversight for unauthorized filesystem access.
The technical flaw stems from the kernel's improper handling of mount flags during unmount operations within user namespaces. When a process executes umount2 with the MNT_DETACH flag, the kernel should verify that the MNT_LOCKED flag is not set before proceeding with the unmount operation. However, this validation check is absent, creating a pathway for local attackers to manipulate mount points and gain access to filesystem locations that should otherwise be restricted. The vulnerability becomes particularly dangerous when combined with user namespace capabilities, as it allows unprivileged users to bypass intended access controls and navigate to protected filesystem areas.
This vulnerability has significant operational impact within Linux environments, as it enables local privilege escalation attacks that can potentially lead to full system compromise. An attacker with low-privilege access can exploit this weakness to gain unauthorized access to restricted filesystem locations, potentially accessing sensitive data or system files that should be protected by mount restrictions. The attack vector is particularly concerning because it operates within the kernel's core mount management functions, making it difficult to detect and mitigate through traditional application-level security measures. The vulnerability aligns with CWE-284, which addresses improper access control in software systems, and represents a classic example of insufficient privilege checking in kernel space operations.
The exploitation of this vulnerability demonstrates how seemingly minor oversights in kernel code can create substantial security risks, particularly when combined with modern Linux security features like user namespaces. Attackers can leverage this weakness to escalate privileges and access filesystem locations that should be restricted to privileged users or specific processes. The impact extends beyond simple data access, as successful exploitation can enable further attacks including privilege escalation to root access and potential lateral movement within compromised systems. Organizations running affected kernel versions are particularly vulnerable, as the attack requires only local access and can be executed by any user with basic system privileges.
Mitigation strategies for CVE-2014-9717 require immediate kernel upgrades to version 4.0.2 or later, where the fix properly validates mount flags during MNT_DETACH operations. System administrators should prioritize patching affected systems and monitor for any signs of exploitation attempts. Additional protective measures include restricting user namespace creation capabilities where possible, implementing proper access controls, and maintaining comprehensive system monitoring to detect unauthorized mount operations. The vulnerability serves as a reminder of the critical importance of thorough code review and testing of kernel-level operations, particularly those involving privilege management and access control mechanisms. Organizations should also consider implementing runtime protection measures and security monitoring solutions that can detect anomalous mount behavior and potential exploitation attempts.