In the Linux kernel, the following vulnerability has been resolved: nfsd: convert nfsd_net boolean flags to unsigned long flags word nfsd_net contains several boolean fields that are accessed from concurrent contexts without serialization. In particular, nfsd4_end_grace() guards its drain path with a plain bool: if (nn->grace_ended) return; nn->grace_ended = true; The read and the write are independent, and nothing in struct nfsd_net serializes them. At least two contexts can reach this code with no lock held: laundromat path laundry_wq kworker nfs4_laundromat() nfsd4_end_grace() RECLAIM_COMPLETE path nfsd compound kthread nfsd4_reclaim_complete() inc_reclaim_complete() nfsd4_end_grace() Both callers can observe grace_ended == false on different CPUs, both store true, and both proceed into nfsd4_record_grace_done(), which invokes the active client_tracking_ops->grace_done callback. For tracking ops that drain reclaim_str_hashtbl (legacy_tracking_ops via nfsd4_recdir_purge_old, and the cld v1+ ops via nfsd4_cld_grace_done), grace_done calls nfs4_release_reclaim(), which walks every bucket of reclaim_str_hashtbl with no lock and calls nfs4_remove_reclaim_record() (list_del + kfree) on each entry. Two concurrent walkers corrupt the list and double-free every nfs4_client_reclaim. A concurrent nfsd4_find_reclaim_client() iterating the same bucket reads through freed memory. A third call site exists in nfs4_state_start_net() on the skip_grace startup path, but it runs under nfsd_mutex before any client has connected and before the laundromat's first delayed work fires, so it cannot race with the two callers above. Replace the scattered boolean fields in nfsd_net with a single unsigned long flags word and an enum nfsd_net_flag for the bit positions. The grace_ended race is fixed by using test_and_set_bit(), which is atomic on all architectures. The remaining flags (grace_end_forced, in_grace, somebody_reclaimed, track_reclaim_completes, nfsd_net_up, lockd_up) are converted to use test_bit/set_bit/clear_bit for consistency. This avoids sub-word cmpxchg issues on architectures like Hexagon that only support word-sized atomic operations.

An update of the linux package has been released.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - nfsd: convert nfsd_net boolean flags to unsigned long flags word nfsd_net contains several boolean fields     that are accessed from concurrent contexts without serialization. In particular, nfsd4_end_grace() guards     its drain path with a plain bool: if (nn->grace_ended) return; nn->grace_ended = true; The read and the     write are independent, and nothing in struct nfsd_net serializes them. At least two contexts can reach     this code with no lock held: laundromat path laundry_wq kworker nfs4_laundromat() nfsd4_end_grace()     RECLAIM_COMPLETE path nfsd compound kthread nfsd4_reclaim_complete() inc_reclaim_complete()     nfsd4_end_grace() Both callers can observe grace_ended == false on different CPUs, both store true, and     both proceed into nfsd4_record_grace_done(), which invokes the active client_tracking_ops->grace_done     callback. For tracking ops that drain reclaim_str_hashtbl (legacy_tracking_ops via nfsd4_recdir_purge_old,     and the cld v1+ ops via nfsd4_cld_grace_done), grace_done calls nfs4_release_reclaim(), which walks every     bucket of reclaim_str_hashtbl with no lock and calls nfs4_remove_reclaim_record() (list_del + kfree) on     each entry. Two concurrent walkers corrupt the list and double-free every nfs4_client_reclaim. A     concurrent nfsd4_find_reclaim_client() iterating the same bucket reads through freed memory. A third call     site exists in nfs4_state_start_net() on the skip_grace startup path, but it runs under nfsd_mutex before     any client has connected and before the laundromat's first delayed work fires, so it cannot race with the     two callers above. Replace the scattered boolean fields in nfsd_net with a single unsigned long flags word     and an enum nfsd_net_flag for the bit positions. The grace_ended race is fixed by using     test_and_set_bit(), which is atomic on all architectures. The remaining flags (grace_end_forced, in_grace,     somebody_reclaimed, track_reclaim_completes, nfsd_net_up, lockd_up) are converted to use     test_bit/set_bit/clear_bit for consistency. This avoids sub-word cmpxchg issues on architectures like     Hexagon that only support word-sized atomic operations. (CVE-2026-93221)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
376443	Ubuntu 24.04 LTS / 26.04 LTS : Linux kernel vulnerabilities (USN-8959-1)	Nessus	Ubuntu Local Security Checks	Local	high
375039	Photon OS 5.0: Linux PHSA-2026-5.0-92-1047	Nessus	PhotonOS Local Security Checks	Local	high
350104	Linux Distros Unpatched Vulnerability : CVE-2026-93221	Nessus	Misc.	Local	high

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