# CVE-2026-89659

## Summary

- **CVE ID:** CVE-2026-89659
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 13, 2026

## Description

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

NFSD: Prevent client use-after-free during delegation revoke

A delegation stateid holds only a bare pointer to its owning
nfs4_client and does not keep it alive.  The client survives its
stateids only because __destroy_client() drains cl_delegations and
cl_revoked before free_client() runs.

nfs4_laundromat() breaks that invariant: it unhashes an
expired delegation from cl_delegations, drops deleg_lock, then
revoke_delegation() relinks it onto cl_revoked under cl_lock.  In that
window the delegation is on neither list, so client_has_state() can
report no remaining state.

Every teardown path first requires cl_rpc_users to be zero, but
the laundromat holds no such reference.  A client whose recalled
delegation has just timed out can therefore reach free_client()
while revoke_delegation() is still about to dereference cl_lock,
a use-after-free.

Pin the client with cl_rpc_users across the revoke so teardown blocks
until it completes, then reap the delegation from cl_revoked.  A client
already expiring reaps its own, so skip it and leave the delegation on
del_recall_lru.

## Affected Products

- Linux — Linux (3bd64a5ba1719c2bb6cba4493dfd3e23a7653e54)
- Linux — Linux (3.10)
- Linux — Linux (0)
- Linux — Linux (6.18.51)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)

## References

- [CNA](https://git.kernel.org/stable/c/3c0a53ee0b442348d8d2286d6960d3f07bb3a3d3)
- [CNA](https://git.kernel.org/stable/c/2a9d637c2a8fd8ac29ad9b29f28d122ef75c1a56)
- [CNA](https://git.kernel.org/stable/c/4683ca76b3b7e5808338491c6eb3c20e6b4894d5)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.43%
- **EPSS Percentile:** 37.1

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._