A clock domain mismatch vulnerability in the Linux kernel NFS implementation allows unauthenticated remote attackers to trigger a permanent denial of service condition.

The vulnerability exists in the nfsd module within the clients_still_reclaiming function, where an incorrect comparison between CLOCK_REALTIME and CLOCK_BOOTTIME causes grace period calculations to fail. This allows an unauthenticated attacker to hold the NFS server in a grace period indefinitely by sending crafted CLAIM_PREVIOUS OPEN requests.

Successful exploitation of this vulnerability results in a total denial of service for the NFS server, as all non-reclaim operations are blocked for all connected clients. Given the CVSS score of 7.5, this high severity flaw poses a significant operational risk to environments relying on NFS for critical data storage and file sharing. Prolonged outages can disrupt essential business services and impede data accessibility across the network.

Immediate Action: Update the Linux kernel to version 6.18.51, 7.2.4, or later versions as provided by your distribution maintainer.

Proactive Monitoring: Monitor NFS server logs for an unusual volume of CLAIM_PREVIOUS OPEN requests or sustained periods where the server remains in a grace state.

Compensating Controls: Restrict network access to the NFS service to trusted clients only using firewall rules or network segmentation to prevent exploitation by external, unauthenticated actors.

Public Exploit Available: Unknown

This vulnerability represents a significant risk to the availability of storage services within Linux-based infrastructures. Administrators should prioritize the application of kernel patches to the specified versions to eliminate the possibility of a permanent denial of service. If patching is not immediately feasible, network-level access controls should be strictly enforced to mitigate the risk of unauthorized exploitation.