CVE-2024-50043 is a vulnerability identified in the Linux kernel's NFS server daemon (nfsd), specifically related to the handling of delegation state IDs (stateid) in the NFSv4 protocol implementation. The vulnerability arises when multiple FREE_STATEID requests are sent for the same delegation stateid. In the function nfsd4_free_stateid(), the kernel attempts to free a delegation stateid under a client lock. However, the code releases this lock before calling nfs4_put_stid(), which decrements the reference count and potentially frees the stateid. This lock release allows a race condition where another FREE_STATEID request can find and attempt to free the same stateid again. As a result, this leads to either a use-after-free condition or a reference count underflow. A use-after-free can cause memory corruption, potentially leading to kernel crashes (denial of service) or, in some cases, privilege escalation if exploited carefully. The reference count underflow can similarly destabilize kernel memory management. The vulnerability affects Linux kernel versions identified by the commit hash 3f29cc82a84c23cfd12b903029dd26002ca825f5, indicating a specific code state rather than a broad version range. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The vulnerability is rooted in concurrency and memory management flaws within the NFS server's delegation state handling, which is critical for maintaining client state and access control in NFSv4. This issue is particularly relevant for systems running NFS servers on Linux kernels that have not applied the patch fixing this race condition.

For European organizations, the impact of CVE-2024-50043 depends largely on their use of Linux-based NFS servers. NFS is commonly used in enterprise environments for file sharing and storage solutions. Exploitation of this vulnerability could lead to denial of service (system crashes) on critical file servers, disrupting business operations and potentially causing data unavailability. In more severe scenarios, if an attacker can leverage the use-after-free to execute arbitrary code in kernel space, it could lead to privilege escalation, allowing attackers to gain root access and compromise the entire system. This would have serious confidentiality, integrity, and availability implications. Organizations relying on Linux NFS servers for critical infrastructure, including government agencies, financial institutions, and large enterprises in Europe, could face operational disruptions and increased risk of data breaches. The absence of known exploits reduces immediate risk, but the vulnerability's nature means it could be targeted in the future, especially in environments where NFS is exposed to untrusted networks or where multiple clients can send stateid requests. The impact is heightened in sectors with stringent data protection requirements under GDPR, where service availability and data integrity are paramount.

1. Immediate application of the official Linux kernel patch that addresses the race condition in nfsd4_free_stateid() is critical. Organizations should track their Linux distribution security advisories for updates incorporating this fix. 2. Where patching is not immediately possible, restrict access to NFS servers to trusted networks and clients only, minimizing exposure to potentially malicious FREE_STATEID requests. 3. Implement network-level controls such as firewalls and intrusion detection/prevention systems to monitor and block suspicious NFS traffic patterns indicative of exploitation attempts. 4. Conduct thorough auditing and monitoring of NFS server logs for unusual stateid operations or repeated FREE_STATEID requests that could signal exploitation attempts. 5. Consider deploying kernel hardening features such as Kernel Address Space Layout Randomization (KASLR) and Kernel Page Table Isolation (KPTI) to reduce the risk of successful exploitation of memory corruption vulnerabilities. 6. Regularly review and update incident response plans to include scenarios involving kernel-level vulnerabilities and potential NFS service disruptions. 7. Engage with Linux vendor support channels to receive timely updates and guidance on this vulnerability.