CVE-2024-46695 is a vulnerability identified in the Linux kernel affecting the security modules SELinux and Smack, specifically related to the handling of security labels on files within NFS (Network File System) exports. The issue arises because the root user on an NFS client can bypass permission checks and change security labels on files in an NFS filesystem that is exported with root squashing enabled. Root squashing is a security feature intended to map remote root users to a non-privileged user on the NFS server to prevent unauthorized root-level access. However, due to incomplete permission checks in the kernel's implementation, the root user on the client side can still manipulate security attributes, potentially leading to unauthorized access or privilege escalation. The vulnerability stems from the use of the __vfs_setxattr_noperm() function within the nfsd_setattr() code path. This function assumes that the caller has already performed appropriate permission checks and holds the inode mutex lock, but nfsd_setattr() does not fully implement these checks, particularly those enforced by security_inode_setxattr() and related Linux Security Module (LSM) hooks. The fix involves replacing __vfs_setxattr_noperm() with __vfs_setxattr_locked(), which enforces proper locking and permission verification. Additionally, this change causes the NFS daemon to recall conflicting delegations when a client attempts to change a file's security label, further strengthening security. This vulnerability is significant because it allows a privileged user on an NFS client to circumvent intended security restrictions on the server side, potentially altering security contexts and labels that govern access controls. Although exploitation requires root access on the client side, the impact can be severe in environments where NFS is used to share sensitive data and SELinux or Smack policies are critical for enforcing security boundaries. No known exploits are currently reported in the wild, and the vulnerability was published on September 13, 2024.

For European organizations, the impact of CVE-2024-46695 can be considerable, especially for those relying heavily on NFS for file sharing in multi-user or multi-tenant environments, such as research institutions, cloud service providers, and enterprises with distributed Linux infrastructure. The ability for a root user on an NFS client to modify security labels on files could lead to unauthorized access to sensitive data, bypassing mandatory access controls enforced by SELinux or Smack. This could result in data breaches, compromise of system integrity, and potential lateral movement within networks. Organizations operating in regulated sectors such as finance, healthcare, and critical infrastructure may face compliance violations if such unauthorized changes lead to data exposure or system compromise. Furthermore, the vulnerability could undermine trust in security policies and complicate incident response efforts due to altered security contexts. Although exploitation requires root privileges on the client side, insider threats or compromised client machines could leverage this vulnerability to escalate privileges or disrupt security controls on NFS servers.

To mitigate CVE-2024-46695, European organizations should prioritize applying the official Linux kernel patches that replace __vfs_setxattr_noperm() with __vfs_setxattr_locked() in the nfsd_setattr() function. This patch ensures proper permission checks and locking mechanisms are enforced. Until patches are applied, organizations should consider the following specific measures: 1. Restrict root access on NFS clients: Limit which users or systems have root privileges on NFS clients to reduce the risk of exploitation. 2. Harden NFS exports: Review and tighten NFS export options, avoiding root squashing configurations where possible or ensuring strict access controls. 3. Monitor security label changes: Implement auditing and monitoring of security label modifications on NFS-mounted filesystems to detect suspicious activity. 4. Use network segmentation: Isolate NFS clients and servers in secure network segments to limit the attack surface. 5. Employ additional access controls: Complement SELinux/Smack policies with other security layers such as mandatory access control policies and file integrity monitoring. 6. Conduct regular security assessments: Perform vulnerability scans and penetration tests focusing on NFS configurations and Linux security modules. These targeted actions, combined with timely patching, will reduce the risk of exploitation and help maintain the integrity of security policies enforced via SELinux and Smack on NFS shares.