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VulnerabilityPublished Updated

CVE-2025-39977: Linux kernel · futex: Prevent use-after-free during requeue-PI

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · CVSS 7.8 High · fixed in d824b2dbdcfe3c390278dd9652ea526168ef6850 : patch Linux kernel soon.

Data as of 10 Nov 2026, 14:47 UTC

CVSS 3.1 base score
7.8High
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (Linux)CVSS 3.17.8
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact
Total control over the software or total information disclosure

CISA SSVC assessment, 2026-10-15.

Patch
Available – fixed in d824b2dbdcfe3c390278dd9652ea526168ef6850, cb5d19a61274b51b49601214a87af573b43d60fa, b549113738e8c751b613118032a724b772aa83f2 +2
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 15 Oct 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
LinuxLinuxAffected
  • ≥ 07d91ef510fb16a2e0ca7453222105835b7ba3b8, < d824b2dbdcfe3c390278dd9652ea526168ef6850
Fixed in
  • d824b2dbdcfe3c390278dd9652ea526168ef6850
LinuxLinuxAffected
  • ≥ 07d91ef510fb16a2e0ca7453222105835b7ba3b8, < cb5d19a61274b51b49601214a87af573b43d60fa
Fixed in
  • cb5d19a61274b51b49601214a87af573b43d60fa
LinuxLinuxAffected
  • ≥ 07d91ef510fb16a2e0ca7453222105835b7ba3b8, < b549113738e8c751b613118032a724b772aa83f2
Fixed in
  • b549113738e8c751b613118032a724b772aa83f2
LinuxLinuxAffected
  • ≥ 07d91ef510fb16a2e0ca7453222105835b7ba3b8, < a170b9c0dde83312b8b58ccc91509c7c15711641
Fixed in
  • a170b9c0dde83312b8b58ccc91509c7c15711641
LinuxLinuxAffected
  • ≥ 07d91ef510fb16a2e0ca7453222105835b7ba3b8, < 348736955ed6ca6e99ca24b93b1d3fbfe352c181
Fixed in
  • 348736955ed6ca6e99ca24b93b1d3fbfe352c181
LinuxLinuxAffected
  • =5.15
Fixed in–

AI-suggested

A fix for this vulnerability has been implemented and is available in the Linux kernel. Users and administrators should update to the fixed kernel versions identified by the commits d824b2dbdcfe3c390278dd9652ea526168ef6850, cb5d19a61274b51b49601214a87af573b43d60fa, b549113738e8c751b613118032a724b772aa83f2, a170b9c0dde83312b8b58ccc91509c7c15711641, and 348736955ed6ca6e99ca24b93b1d3fbfe352c181. No additional mitigation steps are indicated beyond applying the official patch.

Description

CVE-2025-39977 is a high-severity use-after-free vulnerability in the Linux kernel's futex subsystem affecting version 5.15. It arises from a race condition during the requeue-PI operation where synchronization is improperly handled, potentially leading to use of freed memory. The flaw was triggered by syzbot and involves the futex_q structure's task pointer being accessed unsafely during state updates. The issue is resolved by ensuring futex_q::task is read before updating the requeue state, leveraging existing spinlock and RCU protections to maintain task_struct validity during wakeup.

References

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