CVE-2021-46942

Local service hang via miscounted SQPOLL requests

Published Feb 27, 2024 · Updated May 11, 2026

Denial of service in Linux 5.12 through 5.12.2 allows local users to hang io_uring SQPOLL cancellation via shared contexts. io_uring_cancel_sqpoll uses per-task inflight counters while canceling one context, so shared contexts make it wait for requests that cannot arrive. A local user must operate shared SQPOLL contexts; cancellation can then block a kernel task indefinitely and interrupt service.

CVSS severity5.5
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Linux 5.12 through 5.12.2 allows local users to hang io_uring SQPOLL cancellation via shared contexts. io_uring_cancel_sqpoll uses per-task inflight counters while canceling one context, so shared contexts make it wait for requests that cannot arrive. A local user must operate shared SQPOLL contexts; cancellation can then block a kernel task indefinitely and interrupt service.

The record

CVE
CVE-2021-46942
Published
Feb 27, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 27, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=37d1e2e3642e2380750d7f35279180826f29660e <734551df6f9bedfbefcd113ede665945e9de0b99
  2. Affected versionversion=37d1e2e3642e2380750d7f35279180826f29660e <cb5e0b3d0f993a6268c1a2c7ede2f9aa0c17ef68
  3. Affected versionversion=5.12

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=37d1e2e3642e2380750d7f35279180826f29660e <734551df6f9bedfbefcd113ede665945e9de0b99; version=37d1e2e3642e2380750d7f35279180826f29660e <cb5e0b3d0f993a6268c1a2c7ede2f9aa0c17ef68; version=5.12

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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