---
id: CVE-2026-89689
title: 'nfsd: don''t free session slots that are still in use'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  nfsd: don't free session slots that are still in use

  nfsd4_sequence() can free the very slot it is currently processing.
  When the session shrinker has reduced se_targe…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
cwe:
  - CWE-825
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 <
    72d40b103bb03f0124d3a3c8f71a30cbafaf6afa
  - >-
    Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 <
    b449b134e7762ddf98653a4b1d3e76d2d212ea64
  - >-
    Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 <
    f5d22e372f4ac3eb287037a488c29691d52a6330
  - Linux 6.14
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:51:02.559Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89689'
references:
  - url: 'https://git.kernel.org/stable/c/72d40b103bb03f0124d3a3c8f71a30cbafaf6afa'
  - url: 'https://git.kernel.org/stable/c/b449b134e7762ddf98653a4b1d3e76d2d212ea64'
  - url: 'https://git.kernel.org/stable/c/f5d22e372f4ac3eb287037a488c29691d52a6330'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89689.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89689'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532497'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89689'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89689'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89689.mbox
  - url: 'https://access.redhat.com/errata/RHSA-2026:83207'
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.00614
epssPercentile: 0.492
patched:
  - 10base_smtv
  - enterprise_linux_appstream_v_10
  - enterprise_linux_baseos_v_10
  - enterprise_linux_codeready_linux_builder_v_10
  - enterprise_linux_hidden_v_10
  - enterprise_linux_real_time_for_nfv_v_10
  - enterprise_linux_real_time_v_10
scores:
  cna: 9.8
  vendor: 7
ingestedAt: '2026-09-14T15:23:07.473Z'
---

## Overview

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

nfsd: don't free session slots that are still in use

nfsd4_sequence() can free the very slot it is currently processing.
When the session shrinker has reduced se_target_maxslots below
se_fchannel.maxreqs, the shrink path checks three conditions before
calling free_session_slots():

  1. se_target_maxslots < maxreqs  (shrink was advertised)
  2. slot->sl_generation == se_slot_gen  (slot is up-to-date)
  3. seq->maxslots <= se_target_maxslots  (client acknowledges)

However, seq->slotid is never checked against se_target_maxslots.
A client using a slot in the range [se_target_maxslots, maxreqs) can
satisfy all three conditions: its slot has the current generation
(set by a prior SEQUENCE), and it sends sa_highest_slotid <=
se_target_maxslots to acknowledge the reduction.

free_session_slots() then kfrees every slot at index >=
se_target_maxslots, including the caller's own slot. The function
continues to write sl_seqid, sl_flags, sl_generation, and stores the
dangling pointer in cstate->slot. Later, nfsd4_store_cache_entry()
copies up to maxresp_cached bytes of the compound reply into the freed
sl_data[] array, corrupting whatever slab object now occupies that
address.

Additionally, a concurrent thread processing SEQUENCE on a different
high-numbered slot can have its slot freed out from under it.
NFSD4_SLOT_INUSE is set under nn->client_lock before the lock is
released, so any concurrent thread past SEQUENCE will have its slot
marked. However, free_session_slots() does not check NFSD4_SLOT_INUSE
before freeing.

Fix both problems by:
 1. Checking that the current request's slotid is below the shrink
    boundary.
 2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and
    deferring the shrink if any are active.

## Affected

- `Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < 72d40b103bb03f0124d3a3c8f71a30cbafaf6afa`
- `Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < b449b134e7762ddf98653a4b1d3e76d2d212ea64`
- `Linux >= fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7 < f5d22e372f4ac3eb287037a488c29691d52a6330`
- `Linux 6.14`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **RHSA-2026:83207** · Red Hat · fixed in: 10Base-SMTV, Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux BaseOS (v. 10), Red Hat Enterprise Linux CodeReady Linux Builder (v. 10), Red Hat Enterprise Linux Hidden (v. 10), Red Hat Enterprise Linux Real Time for NFV (v. 10), … · released 2026-10-15 · [advisory](https://access.redhat.com/errata/RHSA-2026:83207)
- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 6 · updated 2026-10-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89689.json)