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Response snapshot Nov 2, 2026, 17:11 UTC

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VulnerabilityCVE-2026-99227

Linux kernel: io_uring/waitid: prevent cancel reference wrap

In the Linux kernel, the following vulnerability has been resolved: io_uring/waitid: prevent cancel reference wrap io_waitid packs the cancellation state into bit 31 of ->refs and uses bits 30:0 as a 31-bit reference counter: #define IO_WAITID_CANCEL_FLAG BIT(31) #define IO_WAITID_REF_MASK GENMASK(30, 0) __io_waitid_cancel() marks a request canceled, then increments the low bits of ->refs to claim completion ownership.

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-2026-99227 (opens a new tab)

What happened

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

io_uring/waitid: prevent cancel reference wrap

io_waitid packs the cancellation state into bit 31 of ->refs and uses bits 30:0 as a 31-bit reference counter:

#define IO_WAITID_CANCEL_FLAG BIT(31) #define IO_WAITID_REF_MASK GENMASK(30, 0)

Continue reading

__io_waitid_cancel() marks a request canceled, then increments the low bits of ->refs to claim completion ownership. When another path owns the request, the increment remains even though cancellation returns false. The request remains discoverable by cancellation, so repeated failed attempts can wrap the 31-bit reference field to zero. A later cancellation can claim ownership and complete the request a second time.

Use atomic_fetch_or() when setting the cancel flag and inspect the old flag value. The first cancel attempt continues to the existing ownership increment, preserving its wake and issuer handoff semantics. Later attempts see the cancel flag and return without incrementing the reference field.

This makes repeated failed cancellation attempts idempotent while leaving the first-cancel state transitions unchanged.

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-2026-99227 (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: prevent cancel reference wrap (CVE-2026-99227). https://kevwire.com/record/CVE-2026-99227

MLA

"Linux kernel: io_uring/waitid: prevent cancel reference wrap (CVE-2026-99227)." KEVWire, 2 Nov. 2026, kevwire.com/record/CVE-2026-99227.

Chicago

KEVWire. "Linux kernel: io_uring/waitid: prevent cancel reference wrap (CVE-2026-99227)." Last modified November 2, 2026. https://kevwire.com/record/CVE-2026-99227.

Evidence summary (plain text)

Linux kernel: io_uring/waitid: prevent cancel reference wrap (Nov 2, 2026).
In the Linux kernel, the following vulnerability has been resolved:

io_uring/waitid: prevent cancel reference wrap

io_waitid packs the cancellation state into bit 31 of ->refs and uses
bits 30:0 as a 31-bit reference counter:

  #define IO_WAITID_CANCEL_FLAG BIT(31)
  #define IO_WAITID_REF_MASK    GENMASK(30, 0)

__io_waitid_cancel() marks a request canceled, then increments the low
bits of ->refs to claim completion ownership. When another path owns the
request, the increment remains even though cancellation returns false.
CVSS 7.8 (version 3.1; evidence as of Nov 2, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-99227).
Sources:
NVD CVE-2026-99227: https://nvd.nist.gov/vuln/detail/CVE-2026-99227
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-2026-99227.
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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