CVE-2025-21795

In the Linux kernel, the following vulnerability has been resolved:

NFSD: fix hang in nfsd4_shutdown_callback

If nfs4_client is in courtesy state then there is no point to send the callback. This causes nfsd4_shutdown_callback to hang since cl_cb_inflight is not 0. This hang lasts about 15 minutes until TCP notifies NFSD that the connection was dropped.

This patch modifies nfsd4_run_cb_work to skip the RPC call if nfs4_client is in courtesy state.

This vulnerability is rated as Moderate impact for Red Hat Enterprise Linux because exploitation is limited to systems actively serving NFSv4 shares where client sessions transition into a courtesy state, causing a temporary denial of service rather than code execution or privilege escalation. The issue only manifests on hosts configured and running the kernel NFS server daemon, which is not enabled by default on standard installations. When triggered, the resulting stall affects NFS callback processing and delays shutdown routines for up to fifteen minutes until connection timeouts expire, without compromising system integrity or confidentiality.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.