---
id: CVE-2026-89696
title: 'nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref

  When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return
  success with fh_dentry and fh…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
cwe:
  - CWE-476
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    00c84f4eec715e501efc080a5670114189e42507
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    2d9846fd1c767920fddd4bde30eb35cd2969df13
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    977e6f006a7a3ffc4216ae6034f768f8de6fd138
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    35f248bd40b47b229d4999581df45b97daadd977
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    311f7d926630940650447cbd1c932b076b40a6c4
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    bf4d338dc8625d70c7f2cb0657d66851a7ac9154
  - >-
    Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e <
    c59738a00aa51b16adc1b5ceb7c80877168efb4d
  - Linux 5.6
published: '2026-09-11'
updated: '2026-10-19'
sourceUpdated: '2026-10-19T08:51:09.479Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89696'
references:
  - url: 'https://git.kernel.org/stable/c/ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32'
  - url: 'https://git.kernel.org/stable/c/00c84f4eec715e501efc080a5670114189e42507'
  - url: 'https://git.kernel.org/stable/c/2d9846fd1c767920fddd4bde30eb35cd2969df13'
  - url: 'https://git.kernel.org/stable/c/977e6f006a7a3ffc4216ae6034f768f8de6fd138'
  - url: 'https://git.kernel.org/stable/c/35f248bd40b47b229d4999581df45b97daadd977'
  - url: 'https://git.kernel.org/stable/c/311f7d926630940650447cbd1c932b076b40a6c4'
  - url: 'https://git.kernel.org/stable/c/bf4d338dc8625d70c7f2cb0657d66851a7ac9154'
  - url: 'https://git.kernel.org/stable/c/c59738a00aa51b16adc1b5ceb7c80877168efb4d'
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89696.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89696'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532408'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89696'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89696'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89696.mbox
tags:
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.00752
epssPercentile: 0.54837
scores:
  cna: 7.5
  vendor: 5.5
ingestedAt: '2026-09-14T15:23:07.449Z'
---

## Overview

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

nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref

When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return
success with fh_dentry and fh_export both NULL if fh_verify() returns
nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag
is set, but the compound dispatch loop only uses this flag to bypass
the nfserr_nofilehandle check -- it does not prevent subsequent ops
from running with a NULL fh_dentry.

A remote client can exploit this by crafting a COMPOUND that includes
an inter-SSC COPY (which causes check_if_stalefh_allowed() to set
no_verify=true on the saved PUTFH) with an additional op inserted
between the source PUTFH and SAVEFH. For example, SETATTR calls
fh_want_write() which dereferences fh_export->ex_path.mnt without
calling fh_verify() first, causing a NULL pointer dereference in the
nfsd kthread.

Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set
and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow)
and ops with ALLOWED_WITHOUT_FH (which don't need a resolved
filehandle) may proceed. All other ops receive nfserr_stale, per
RFC 7862 Section 15.2.3 which specifies that foreign filehandle
validation is deferred to the consuming operation and NFS4ERR_STALE
returned at that point.

## Affected

- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < ffdc844e673d2bcb2af8c8c3eef8cdea59d0bf32`
- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < 00c84f4eec715e501efc080a5670114189e42507`
- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < 2d9846fd1c767920fddd4bde30eb35cd2969df13`
- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < 977e6f006a7a3ffc4216ae6034f768f8de6fd138`
- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < 35f248bd40b47b229d4999581df45b97daadd977`
- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < 311f7d926630940650447cbd1c932b076b40a6c4`
- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < bf4d338dc8625d70c7f2cb0657d66851a7ac9154`
- `Linux >= b9e8638e3d9ed8334f1f7071e081860aac37e83e < c59738a00aa51b16adc1b5ceb7c80877168efb4d`
- `Linux 5.6`

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · updated 2026-09-21 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89696.json)