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.

Metrics

No CVSS v4.0

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00193.

Key SSVC decision points have not yet been added.

Affected Vendors & Products

Vendors Products
Linux
  • Linux Kernel

No data.

No data.

OpenCVE Enrichment is a feature of OpenCVE that uses AI to automatically link vendors and products to CVEs. Learn more on GitHub.

Vendors Products
Linux
  • Linux Kernel
References
Link Providers
https://cert-portal.siemens.com/productcert/html/ssa-082556.html cve-icon
https://git.kernel.org/stable/c/348736955ed6ca6e99ca24b93b1d3fbfe352c181 cve-icon cve-icon
https://git.kernel.org/stable/c/a170b9c0dde83312b8b58ccc91509c7c15711641 cve-icon cve-icon
https://git.kernel.org/stable/c/b549113738e8c751b613118032a724b772aa83f2 cve-icon cve-icon
https://git.kernel.org/stable/c/cb5d19a61274b51b49601214a87af573b43d60fa cve-icon cve-icon
https://git.kernel.org/stable/c/d824b2dbdcfe3c390278dd9652ea526168ef6850 cve-icon cve-icon
https://lore.kernel.org/linux-cve-announce/2025101558-CVE-2025-39977-b3a2@gregkh/T cve-icon
https://nvd.nist.gov/vuln/detail/CVE-2025-39977 cve-icon
https://www.cve.org/CVERecord?id=CVE-2025-39977 cve-icon
History

Thu, 30 Jul 2026 06:15:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

 cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Tue, 12 May 2026 13:30:00 +0000

Type Values Removed Values Added
References

Mon, 11 May 2026 22:30:00 +0000

Type Values Removed Values Added
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*

Mon, 20 Oct 2025 13:30:00 +0000

Type Values Removed Values Added
First Time appeared Linux
Linux linux Kernel
Vendors & Products Linux
Linux linux Kernel

Thu, 16 Oct 2025 12:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 7.0, 'vector': 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

threat_severity

Moderate

Wed, 15 Oct 2025 08:00:00 +0000

Type Values Removed Values Added
Description 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.
Title futex: Prevent use-after-free during requeue-PI
References
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-07-30T05:59:08.623Z

Reserved: 2025-04-16T07:20:57.150Z

Link: CVE-2025-39977

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Deferred

Published: 2025-10-15T08:15:35.517

Modified: 2026-06-17T09:18:56.690

Link: CVE-2025-39977

cve-icon Redhat

Severity : Moderate

Publid Date: 2025-10-15T00:00:00Z

Links: CVE-2025-39977 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2025-10-20T13:26:49Z