CVE-2014-5207 in Linux
Summary
by MITRE
fs/namespace.c in the Linux kernel through 3.16.1 does not properly restrict clearing MNT_NODEV, MNT_NOSUID, and MNT_NOEXEC and changing MNT_ATIME_MASK during a remount of a bind mount, which allows local users to gain privileges, interfere with backups and auditing on systems that had atime enabled, or cause a denial of service (excessive filesystem updating) on systems that had atime disabled via a "mount -o remount" command within a user namespace.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 11/25/2024
The vulnerability described in CVE-2014-5207 resides within the Linux kernel's namespace handling mechanisms, specifically in the fs/namespace.c file affecting kernel versions through 3.16.1. This flaw represents a privilege escalation vulnerability that exploits improper restrictions during filesystem remount operations on bind mounts. The issue occurs when a user namespace performs a remount operation, allowing local attackers to manipulate critical mount flags that control filesystem behavior and security policies.
The technical implementation of this vulnerability stems from the kernel's insufficient validation of mount flag modifications during remount operations on bind mounts. Specifically, the kernel fails to properly restrict the clearing of three critical mount flags: MNT_NODEV which prevents device file access, MNT_NOSUID which disables setuid bit interpretation, and MNT_NOEXEC which prevents execution of binaries from the filesystem. Additionally, the vulnerability allows modification of MNT_ATIME_MASK which controls access time updating behavior. These restrictions are particularly problematic because they operate within user namespaces, where unprivileged users can potentially escalate their privileges.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass broader system security and stability concerns. Attackers can leverage this flaw to gain elevated privileges within the confines of a user namespace, potentially allowing them to bypass security controls that would normally prevent unauthorized access to system resources. The ability to interfere with backup and auditing operations becomes particularly dangerous when atime is enabled, as malicious users can manipulate access time tracking mechanisms to hide their activities or disrupt forensic analysis. Systems with atime disabled face potential denial of service conditions through excessive filesystem updating, as the vulnerability can cause continuous write operations that degrade system performance.
This vulnerability directly maps to CWE-264, which addresses permissions, privileges, and access controls in software systems, and aligns with several ATT&CK techniques including privilege escalation through kernel vulnerabilities and defense evasion by manipulating filesystem access controls. The exploitability of this issue is enhanced by the fact that it operates within user namespaces, making it accessible to unprivileged users who can create isolated environments where these kernel-level privileges can be abused. Organizations should consider implementing kernel hardening measures, monitoring for unusual mount operations, and ensuring timely patching of affected kernel versions to prevent exploitation of this vulnerability that could lead to complete system compromise.