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

NFSD: Prevent post-shutdown use-after-free in unlock_filesystem

Writing a filesystem path to /proc/fs/nfsd/unlock_filesystem runs
nfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the
handler confirms that nn->nfsd_serv is set. Once nfsd has shut down,
nfs4_state_destroy_net() has freed nn->conf_id_hashtbl but left the
pointer intact, so the cancel helper iterates freed slab memory as an
array of struct list_head and then dereferences a bogus nfs4_client
when it takes clp->async_lock. A local administrator holding
CAP_SYS_ADMIN can reach this use-after-free by stopping the server and
then writing to unlock_filesystem; KASAN reports a slab-use-after-free
read in nfsd4_cancel_copy_by_sb().

nfsd4_revoke_states() walks the same state tables and for that reason
already runs only under nfsd_mutex with nn->nfsd_serv confirmed
present. Move the async COPY cancel into that protected section so
every NFSv4 state-table walker on this path observes a running server.
Async copies exist only while the server runs, so gating the cancel on
nn->nfsd_serv loses nothing.
Published: 2026-09-11
Score: 4.1 Medium
EPSS: n/a
KEV: No
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Remediation

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History

Sat, 12 Sep 2026 00:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-825
References
Metrics threat_severity

None

 cvssV3_1

{'score': 4.1, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Important

Fri, 11 Sep 2026 23:45:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent post-shutdown use-after-free in unlock_filesystem Writing a filesystem path to /proc/fs/nfsd/unlock_filesystem runs nfsd4_cancel_copy_by_sb() before nfsd_mutex is held and before the handler confirms that nn->nfsd_serv is set. Once nfsd has shut down, nfs4_state_destroy_net() has freed nn->conf_id_hashtbl but left the pointer intact, so the cancel helper iterates freed slab memory as an array of struct list_head and then dereferences a bogus nfs4_client when it takes clp->async_lock. A local administrator holding CAP_SYS_ADMIN can reach this use-after-free by stopping the server and then writing to unlock_filesystem; KASAN reports a slab-use-after-free read in nfsd4_cancel_copy_by_sb(). nfsd4_revoke_states() walks the same state tables and for that reason already runs only under nfsd_mutex with nn->nfsd_serv confirmed present. Move the async COPY cancel into that protected section so every NFSv4 state-table walker on this path observes a running server. Async copies exist only while the server runs, so gating the cancel on nn->nfsd_serv loses nothing.
Title NFSD: Prevent post-shutdown use-after-free in unlock_filesystem
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-09-11T19:45:49.086Z

Reserved: 2026-09-11T19:38:34.744Z

Link: CVE-2026-89661

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-11T20:19:52.413

Modified: 2026-09-11T20:19:52.413

Link: CVE-2026-89661

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-11T19:45:49Z

Links: CVE-2026-89661 - Bugzilla

cve-icon OpenCVE Enrichment

No data.

Weaknesses