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Response snapshot Nov 2, 2026, 17:11 UTC

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VulnerabilityCVE-2026-99231

Linux kernel: io_uring/waitid: own the request before clearing ->head

In the Linux kernel, the following vulnerability has been resolved: io_uring/waitid: own the request before clearing ->head io_waitid_remove_wq() only takes the wait queue lock if ->head is set.

At a glance

Exploited
Not known
Severity
7.8 High (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

Check the vendor advisory for affected versions and fixes.

Read NVD CVE-2026-99231 (opens a new tab)

What happened

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

io_uring/waitid: own the request before clearing ->head

io_waitid_remove_wq() only takes the wait queue lock if ->head is set. io_waitid_wait() clears ->head first thing, before it tries to become the owner of the request by bumping ->refs. If somebody else owns the request at that point, nothing keeps it from completing the request while the wake up handler is still going to touch it:

CPU0 (io_waitid_wait) CPU1 (io_waitid, holds a ref) list_del_init(&wait->entry) smp_store_release(&iw->head, NULL) __do_wait() finds another child io_waitid_remove_wq() // ->head == NULL, no locking io_waitid_finish(), IOU_COMPLETE // request freed and reused atomic_fetch_inc(&iw->refs)

Continue reading

The same goes for __io_waitid_cancel() if it claims the request in that window. ->refs is part of the per opcode data of the request, so this increments whatever the next user of the request keeps there. If that happens to be zero, the handler concludes that it owns the request, and queues io_waitid_cb() for it. With the window held open by a delay, and the request reused for a receive that is waiting for data:

BUG: KASAN: slab-use-after-free in __wake_up_common+0x1ca/0x1f0 __wake_up_sync_key+0x36/0x50 sock_def_readable+0xf1/0x420 unix_stream_sendmsg+0x60b/0x1110 Allocated by task 87: io_arm_apoll+0x1ed/0x940 Freed by task 87: __io_submit_flush_completions+0x118d/0x1a10 tctx_task_work_run+0x327/0x950

Only clear ->head once the handler owns the request. If it doesn't, the owner finds ->head set and has to wait for the lock, which is held by the caller of the handler. Deleting the already deleted entry again is harmless.

Scores and how they were measured

CVSS base severity

7.8

Version 3.1As of

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    NVD CVE-2026-99231 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  2. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  3. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 2). Linux kernel: io_uring/waitid: own the request before clearing ->head (CVE-2026-99231). https://kevwire.com/record/CVE-2026-99231

MLA

"Linux kernel: io_uring/waitid: own the request before clearing ->head (CVE-2026-99231)." KEVWire, 2 Nov. 2026, kevwire.com/record/CVE-2026-99231.

Chicago

KEVWire. "Linux kernel: io_uring/waitid: own the request before clearing ->head (CVE-2026-99231)." Last modified November 2, 2026. https://kevwire.com/record/CVE-2026-99231.

Evidence summary (plain text)

Linux kernel: io_uring/waitid: own the request before clearing ->head (Nov 2, 2026).
In the Linux kernel, the following vulnerability has been resolved:

io_uring/waitid: own the request before clearing ->head

io_waitid_remove_wq() only takes the wait queue lock if ->head is set.
io_waitid_wait() clears ->head first thing, before it tries to become the
owner of the request by bumping ->refs.
CVSS 7.8 (version 3.1; evidence as of Nov 2, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-99231).
Sources:
NVD CVE-2026-99231: https://nvd.nist.gov/vuln/detail/CVE-2026-99231
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-02T15:36:06.356Z&lastModEndDate=2026-11-02T17:10:56.063Z&resultsPerPage=500&startIndex=0
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-11-02T15:01:12.608Z&lastModEndDate=2026-11-02T16:35:57.586Z&resultsPerPage=500&startIndex=500
Record ID: CVE-2026-99231.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 2, 2026, 17:10 UTC. Ingestion is not an independent editorial investigation.

NVD status: Received. Publication in the NVD is not evidence of exploitation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

Record detail