CVE-2025-39977

A use-after-free vulnerability was found in the Linux kernel’s futex subsystem where, under a specific race involving threads T1 and T2 (via futex_wait_requeue_pi(), futex_requeue(), futex_requeue_pi_complete() and the wakeup path), the futex_q::lock_ptr synchronization can be bypassed and the task_struct pointer may be used after the object has been freed, leading to memory corruption or kernel instability.

A use-after-free vulnerability was found in the Linux kernel's futex subsystem. If a thread waiting via futex_wait_requeue_pi() is woken by a timeout or signal while another thread concurrently performs a PI requeue via futex_requeue(), the waiting thread can return to user space without proper futex_q::lock_ptr synchronization, and the requeue path may subsequently dereference a task_struct pointer through stale on-stack futex_q data, leading to memory corruption or a kernel panic. A local attacker with the ability to run code on an affected system could exploit this race to crash the kernel, causing a denial of service. Red Hat rates the impact of this flaw as Moderate because exploiting it requires a local user, a narrow timing window (high attack complexity), and the consequence is limited to availability. This differs from the upstream CVE.org severity of Important (CVSS 7.8); Red Hat's severity (CVSS 4.7, CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H) reflects the difficulty of triggering the race and the availability-only impact. The kernel and kernel-rt packages in Red Hat Enterprise Linux 8, 9, and 10 and in Red Hat In-Vehicle OS are affected. Red Hat Enterprise Linux 6 and 7 are not affected because the vulnerable code is not present in those releases. Fixes for the affected products are currently deferred because this use-after-free race condition is difficult to trigger in practice and the assessed severity does not justify the risk and effort of backporting a fix at this time. The residual risk is that a local attacker who can reliably win the race could cause a kernel panic (denial of service).

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.