A flaw in the Linux kernel NFS server allows an unauthenticated remote attacker to cause a denial of service by permanently stalling file delegations, potentially impacting system availability.

This vulnerability resides in the nfsd component, specifically within the delegation recall logic. An unauthenticated attacker can trigger a race condition where the NFSD4_CALLBACK_RUNNING bit is not cleared upon a failed queue attempt, causing subsequent lease breaks to fail silently and stalling NFS operations.

The inability to process delegation recalls results in a denial of service for NFS clients, as conflicting open or lock requests will stall indefinitely. Given the CVSS 3.1 score of 7.5, this high severity vulnerability poses a significant risk to storage availability and operational continuity in environments relying on NFS for critical data access.

Immediate Action: Update the Linux kernel to version 6.18.50, 7.2.4, or later versions where this fix is integrated.

Proactive Monitoring: Monitor system logs for repeated NFS delegation errors or stalled file locks that may indicate exploitation of this kernel flaw.

Compensating Controls: Restrict access to the NFS service to trusted network segments to reduce the attack surface available to unauthorized actors.

Public Exploit Available: No (exploit_available: unknown)

The vulnerability represents a significant risk to NFS availability. Security teams should prioritize patching the kernel across all affected NFS server instances to remediate this logic flaw and restore proper delegation recall functionality.