---
id: CVE-2026-31446
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: fix use-after-free in update_super_work when racing with umount

  Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount
  filesystem") moved ext4…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ext4: fix use-after-free in update_super_work when racing with umount

  Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount
  filesystem") moved ext4…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H'
cwe:
  - CWE-416
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 5.10.114, < 5.11'
  - 'linux_kernel >= 5.15.38, < 5.15.203'
  - 'linux_kernel >= 5.17.6, < 5.18'
  - 'linux_kernel >= 5.18.1, < 6.1.168'
  - 'linux_kernel >= 6.2, < 6.6.131'
  - 'linux_kernel >= 6.7, < 6.12.80'
  - 'linux_kernel >= 6.13, < 6.18.21'
  - 'linux_kernel >= 6.19, < 6.19.11'
  - linux_kernel = 5.18
  - linux_kernel = 7.0
patched:
  - linux_kernel 6.19.11
published: '2026-04-22'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:19:05.747'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31446'
references:
  - url: 'https://git.kernel.org/stable/c/034053378dd81837fd6c7a43b37ee2e58d4f0b4e'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/08b10e6f37fc533a759e9833af0692242e8b3f93'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9449f99ba04f5dd1c8423ad8a90b3651d7240d1d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c4d829737329f2290dd41e290b7d75effdb2a7ff'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c8fe17a1b308c3d8c703ebfb049b325f844342c3'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/c97e282f7bfd0c3554c63d289964a5ca6a1d2ffe'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d15e4b0a418537aafa56b2cb80d44add83e83697'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00139
epssPercentile: 0.03246
ingestedAt: '2026-09-08T15:33:26.990Z'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:09:20.883316Z'
---

## Overview

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

ext4: fix use-after-free in update_super_work when racing with umount

Commit b98535d09179 ("ext4: fix bug_on in start_this_handle during umount
filesystem") moved ext4_unregister_sysfs() before flushing s_sb_upd_work
to prevent new error work from being queued via /proc/fs/ext4/xx/mb_groups
reads during unmount. However, this introduced a use-after-free because
update_super_work calls ext4_notify_error_sysfs() -> sysfs_notify() which
accesses the kobject's kernfs_node after it has been freed by kobject_del()
in ext4_unregister_sysfs():

  update_super_work                ext4_put_super
  -----------------                --------------
                                   ext4_unregister_sysfs(sb)
                                     kobject_del(&sbi->s_kobj)
                                       __kobject_del()
                                         sysfs_remove_dir()
                                           kobj->sd = NULL
                                         sysfs_put(sd)
                                           kernfs_put()  // RCU free
  ext4_notify_error_sysfs(sbi)
    sysfs_notify(&sbi->s_kobj)
      kn = kobj->sd              // stale pointer
      kernfs_get(kn)             // UAF on freed kernfs_node
                                   ext4_journal_destroy()
                                     flush_work(&sbi->s_sb_upd_work)

Instead of reordering the teardown sequence, fix this by making
ext4_notify_error_sysfs() detect that sysfs has already been torn down
by checking s_kobj.state_in_sysfs, and skipping the sysfs_notify() call
in that case. A dedicated mutex (s_error_notify_mutex) serializes
ext4_notify_error_sysfs() against kobject_del() in ext4_unregister_sysfs()
to prevent TOCTOU races where the kobject could be deleted between the
state_in_sysfs check and the sysfs_notify() call.

## Affected

- `linux_kernel >= 5.10.114, < 5.11`
- `linux_kernel >= 5.15.38, < 5.15.203`
- `linux_kernel >= 5.17.6, < 5.18`
- `linux_kernel >= 5.18.1, < 6.1.168`
- `linux_kernel >= 6.2, < 6.6.131`
- `linux_kernel >= 6.7, < 6.12.80`
- `linux_kernel >= 6.13, < 6.18.21`
- `linux_kernel >= 6.19, < 6.19.11`
- `linux_kernel = 5.18`
- `linux_kernel = 7.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.19.11`