---
id: CVE-2025-39977
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  futex: Prevent use-after-free during requeue-PI

  syzbot managed to trigger the following race:

     T1                               T2

   futex_wait_requeue_pi()
     fute…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  futex: Prevent use-after-free during requeue-PI

  syzbot managed to trigger the following race:

     T1                               T2

   futex_wait_requeue_pi()
     fute…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 <
    cb5d19a61274b51b49601214a87af573b43d60fa
  - >-
    Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 <
    348736955ed6ca6e99ca24b93b1d3fbfe352c181
  - >-
    Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 <
    a170b9c0dde83312b8b58ccc91509c7c15711641
  - >-
    Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 <
    d824b2dbdcfe3c390278dd9652ea526168ef6850
  - >-
    Linux >= 07d91ef510fb16a2e0ca7453222105835b7ba3b8 <
    b549113738e8c751b613118032a724b772aa83f2
  - Linux 5.15
published: '2025-10-15'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:18:03.763'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-39977'
references:
  - url: 'https://git.kernel.org/stable/c/348736955ed6ca6e99ca24b93b1d3fbfe352c181'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a170b9c0dde83312b8b58ccc91509c7c15711641'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b549113738e8c751b613118032a724b772aa83f2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/cb5d19a61274b51b49601214a87af573b43d60fa'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/d824b2dbdcfe3c390278dd9652ea526168ef6850'
    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
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-39977.json
  - url: 'https://access.redhat.com/security/cve/CVE-2025-39977'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2404113'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2025-39977'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-39977'
  - url: >-
      https://lore.kernel.org/linux-cve-announce/2025101558-CVE-2025-39977-b3a2@gregkh/T
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.0015
epssPercentile: 0.04134
ingestedAt: '2026-09-08T15:33:26.996Z'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-15T21:55:38.918885Z'
cwe:
  - CWE-416
scores:
  nvd: 7.8
  vendor: 4.7
---

## Overview

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

futex: Prevent use-after-free during requeue-PI

syzbot managed to trigger the following race:

   T1                               T2

 futex_wait_requeue_pi()
   futex_do_wait()
     schedule()
                               futex_requeue()
                                 futex_proxy_trylock_atomic()
                                   futex_requeue_pi_prepare()
                                   requeue_pi_wake_futex()
                                     futex_requeue_pi_complete()
                                      /* preempt */

         * timeout/ signal wakes T1 *

   futex_requeue_pi_wakeup_sync() // Q_REQUEUE_PI_LOCKED
   futex_hash_put()
  // back to userland, on stack futex_q is garbage

                                      /* back */
                                     wake_up_state(q->task, TASK_NORMAL);

In this scenario futex_wait_requeue_pi() is able to leave without using
futex_q::lock_ptr for synchronization.

This can be prevented by reading futex_q::task before updating the
futex_q::requeue_state. A reference on the task_struct is not needed
because requeue_pi_wake_futex() is invoked with a spinlock_t held which
implies a RCU read section.

Even if T1 terminates immediately after, the task_struct will remain valid
during T2's wake_up_state().  A READ_ONCE on futex_q::task before
futex_requeue_pi_complete() is enough because it ensures that the variable
is read before the state is updated.

Read futex_q::task before updating the requeue state, use it for the
following wakeup.

## 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 8, Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9 · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-39977.json)