---
id: "CVE-2026-99252"
kind: "vulnerability"
aliases: ["CVE-2026-99252"]
title: "Linux kernel: io_uring queue push race can stall a high-priority consumer"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["io_uring", "kernel", "linux", "runtime"]
not_affected_if: ["io_uring-disabled", "no-realtime-priority-tasks"]
published_at: "2026-11-03T12:17:31+00:00"
first_seen_at: "2026-11-03T12:20:39+00:00"
updated_at: "2026-11-03T12:22:55+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-99252", "first_seen_at": "2026-11-03T12:20:39+00:00"}]
---

# Linux kernel: io_uring queue push race can stall a high-priority consumer

A race in the Linux kernel's io_uring lockless queue lets a higher-priority task on the same CPU spin forever while a preempted producer has not finished linking a node. The sources describe a hang or denial of service, not code execution or data theft.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the running kernel version with `uname -r` and compare it against the fixed kernel releases in the sources.
- Check whether the system uses io_uring at all, for example whether `io_uring_disabled` is set in `/proc/sys/kernel/io_uring_disabled`.

## Timeline

- 2026-11-03T12:20:39+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-99252

## From the sources

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

io_uring/mpscq: disable preemption while pushing

A push makes the node the new tail, and then links it to its predecessor.
In between the queue isn't empty, but mpscq_pop() can't get at the node.
The consumers deal with that by trying again, with a cond_resched() in
the loop to give a preempted producer the chance to finish.

cond_resched() doesn't do that if the consumer has a higher priority than
the producer and both have to use the same CPU:

  producer (SCHED_OTHER)              consumer (SCHED_FIFO), same CPU
  io_req_local_work_add()
    mpscq_push()
      prev = xchg(&q->tail, node)
  <preempted>                         io_cqring_wait()
                                        __io_run_local_work()
                                      again:
                                          cond_resched()  // nothing to do
                                          mpscq_pop()     // NULL
                                          // work pending, no events yet
                                          goto again

The producer can be any task that is able to queue task_work for the
ring: an io-wq worker, or somebody who sends a message with
IORING_OP_MSG_RING. The consumer spins, holding ->uring_lock, until the
scheduler takes pity on the fair class, which takes about a second with
the default settings of the fair server, and forever without it. The
loops in tctx_task_work_run() and io_cancel_local_task_work() have the
same problem.

Don't allow preemption between the two steps. That bounds the time the
window is open on the CPU of the producer by what interrupts take, and a
consumer that waits for that is on another CPU. The cost is a
preempt_disable()/preempt_enable() pair per push.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_