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

NFSD: Prevent client use-after-free during admin state revocation

A stateid holds only a bare pointer to its nfs4_client; a stateid
reference does not pin it. The client survives only because
__destroy_client() drains its stateids before free_client() runs.

nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(),
which dereferences the client to revoke a stateid and read
clp->cl_minorversion. A teardown racing the dropped lock can free
the client first.

Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and
EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero.
force_expire_client() ignores it: once its wait for cl_rpc_users to
reach zero has passed, a later pin goes unnoticed.

Under client_lock, skip a client whose cl_time is already zero --
force_expire_client() clears it there before waiting -- otherwise pin
cl_rpc_users before dropping the lock. The walk then either sees the
expiry and skips, or pins in time for that wait to cover the revoke.
Published: 2026-09-11
Score: 9.8 Critical
EPSS: < 1% Very Low
KEV: No
Impact: Kernel Use‑After‑Free Exploit
Action: Apply Patch
AI Analysis

Impact

The flaw is in the NFS server’s state revocation logic. When an administrator triggers a revocation, the code releases a lock before the client structure is fully pinned. A state identifier holds only a bare pointer to the client, so if the client is freed first the kernel dereferences dangling memory, resulting in a use‑after‑free condition (CWE‑825). An attacker who can cause or influence such a revocation can execute arbitrary code in kernel mode or crash the system.

Affected Systems

All Linux kernel releases that do not yet contain the patch series referenced in the advisory are vulnerable. The affected code resides in the common NFS server subsystem, so the flaw applies across all supported distributions and kernel versions prior to the commit that removes the race condition.

Risk and Exploitability

The CVSS score of 9.8 indicates a critical risk for privilege escalation or denial of service. The EPSS score of <1% shows that, as of this analysis, exploitation is considered unlikely but not impossible. The vulnerability is not listed in the CISA KEV catalog. Because the description does not explicitly state the attack vector, it is inferred that the exploit requires local or privileged context capable of initiating an admin state revocation; thus the likely attack vector is local with elevated privileges.

Generated by OpenCVE AI on September 15, 2026 at 20:45 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Apply the patch that contains commit 549bd9868e9d77b07ea94870940d64342829c6ad to the NFS subsystem and rebuild the kernel
  • Upgrade the system to a Linux kernel version that includes the NFSD fix, ensuring the kernel package is refreshed from the vendor’s repository
  • If an immediate kernel upgrade is not feasible, disable the NFS server or block admin state revocation operations until the patch can be applied

Generated by OpenCVE AI on September 15, 2026 at 20:45 UTC.

Tracking

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Advisories
Source ID Title
Debian DSA Debian DSA DSA-6528-1 linux security update
History

Mon, 21 Sep 2026 13:30:00 +0000


Sun, 13 Sep 2026 06:45:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}

cvssV3_1

{'score': 9.8, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'}


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

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

None

cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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 client use-after-free during admin state revocation A stateid holds only a bare pointer to its nfs4_client; a stateid reference does not pin it. The client survives only because __destroy_client() drains its stateids before free_client() runs. nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(), which dereferences the client to revoke a stateid and read clp->cl_minorversion. A teardown racing the dropped lock can free the client first. Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero. force_expire_client() ignores it: once its wait for cl_rpc_users to reach zero has passed, a later pin goes unnoticed. Under client_lock, skip a client whose cl_time is already zero -- force_expire_client() clears it there before waiting -- otherwise pin cl_rpc_users before dropping the lock. The walk then either sees the expiry and skips, or pins in time for that wait to cover the revoke.
Title NFSD: Prevent client use-after-free during admin state revocation
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: 2026-09-21T13:14:41.574Z

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

Link: CVE-2026-89660

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-11T20:19:52.300

Modified: 2026-09-21T14:17:24.660

Link: CVE-2026-89660

cve-icon Redhat

Severity : Important

Publid Date: 2026-09-11T19:45:48Z

Links: CVE-2026-89660 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-09-15T21:00:17Z

Weaknesses
  • CWE-825

    Expired Pointer Dereference