CVE-2024-53216 is a high-severity vulnerability in the Linux kernel's NFS daemon (nfsd) subsystem, specifically related to the handling of svc_export and svc_expkey objects used in NFS server exports. The vulnerability arises from improper memory management and synchronization when releasing these objects. The root cause is that the last reference to the cache_head structure can be reduced to zero within the c_show and e_show functions, which use RCU (Read-Copy-Update) read locks. This triggers calls to svc_export_put and expkey_put, which free the ex_uuid memory prematurely. However, subsequent code paths in c_show and e_show still access ex_uuid, causing a use-after-free condition. This is confirmed by Kernel Address Sanitizer (KASAN) reports showing slab-use-after-free errors during procfs reads related to NFS exports. Additionally, the code violates RCU usage rules by sleeping while holding an RCU read lock. Specifically, svc_export_put and expkey_put call path_put, which leads to dput and a sleeping operation, which is unsafe under RCU read lock. The fix involves deferring the freeing of svc_expkey and svc_export objects using rcu_work, which schedules the release asynchronously after an RCU grace period, ensuring safe memory reclamation without sleeping in RCU read-side critical sections. This vulnerability is identified as CWE-416 (Use After Free) and has a CVSS 3.1 score of 7.8, indicating high severity. It requires local privileges (PR:L) but no user interaction (UI:N) and affects confidentiality, integrity, and availability (C:H/I:H/A:H) of the affected systems. Exploitation could allow a local attacker with limited privileges to cause kernel crashes (denial of service) or potentially escalate privileges by exploiting the use-after-free condition in the NFS server kernel module. No known exploits are reported in the wild yet. The affected versions include recent Linux kernel commits prior to the patch, notably kernel version 6.12.0-rc3+ and others in active development branches. The vulnerability impacts Linux systems running NFS server functionality, which is common in enterprise and cloud environments.

For European organizations, this vulnerability poses a significant risk especially for those relying on Linux-based NFS servers for file sharing and storage services. Exploitation could lead to denial of service by crashing the kernel or potentially privilege escalation, allowing attackers to gain unauthorized root access. This could compromise sensitive data confidentiality and integrity, disrupt critical business operations, and impact availability of shared resources. Organizations in sectors such as finance, healthcare, government, and manufacturing that use Linux NFS servers for internal or external file sharing are particularly at risk. The vulnerability requires local access, so insider threats or attackers who have gained limited access could leverage this flaw to escalate privileges or disrupt services. Given the widespread use of Linux in European data centers, cloud providers, and enterprise environments, the impact could be broad if not mitigated promptly. Additionally, the complexity of the bug involving kernel memory management and RCU synchronization means that exploitation could lead to unpredictable system behavior, increasing operational risk.

1. Immediate patching: Apply the official Linux kernel patches that implement the fix using rcu_work to safely release svc_expkey and svc_export objects. Monitor kernel mailing lists and vendor advisories for updated kernel versions addressing CVE-2024-53216. 2. Limit local access: Restrict local user privileges and access to systems running NFS server functionality to trusted personnel only. Use strong authentication and access controls to reduce risk of local exploitation. 3. Disable NFS server if not needed: If NFS server functionality is not required, disable the nfsd service to eliminate the attack surface. 4. Monitor kernel logs: Enable and monitor kernel logs for KASAN or other memory corruption warnings that might indicate exploitation attempts. 5. Use security modules: Employ Linux Security Modules (e.g., SELinux, AppArmor) to confine nfsd processes and limit their capabilities, reducing potential damage from exploitation. 6. Network segmentation: Isolate NFS servers in secure network segments with strict firewall rules to limit exposure. 7. Incident response readiness: Prepare for potential exploitation by having incident response plans and backups in place to recover from denial of service or compromise scenarios.