CVE-2021-46984

Local kernel compromise via preemption-induced context mismatch

Published Feb 28, 2024 · Updated Aug 5, 2026

Out-of-bounds access in the Linux Kyber I/O scheduler allows local users to corrupt kernel memory through block I/O. kyber_bio_merge() obtains a second CPU-local context after __blk_mq_sched_bio_merge() chooses the hardware context, so preemption can pair contexts from different queues and index beyond hctx->nr_ctx. A low-privileged local process must issue I/O to a device using Kyber; the mismatch can disclose or overwrite kernel memory, hijack control flow, or panic the host.

CVSS severity7.8
High
EPSS probability0.26%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds access in the Linux Kyber I/O scheduler allows local users to corrupt kernel memory through block I/O. kyber_bio_merge() obtains a second CPU-local context after __blk_mq_sched_bio_merge() chooses the hardware context, so preemption can pair contexts from different queues and index beyond hctx->nr_ctx. A low-privileged local process must issue I/O to a device using Kyber; the mismatch can disclose or overwrite kernel memory, hijack control flow, or panic the host.

The record

CVE
CVE-2021-46984
Published
Feb 28, 2024
Updated
Aug 5, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-129, T1499.004, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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=4.18
  2. Affected versionversion=a6088845c2bf754d6cb2572b484180680b037804 <0b6b4b90b74c27bea968c214d820ba4254b903a5
  3. Affected versionversion=a6088845c2bf754d6cb2572b484180680b037804 <2ef3c76540c49167a0bc3d5f80d00fd1fc4586df
  4. Affected versionversion=a6088845c2bf754d6cb2572b484180680b037804 <54dbe2d2c1fcabf650c7a8b747601da355cd7f9f
  5. Affected versionversion=a6088845c2bf754d6cb2572b484180680b037804 <a287cd84e047045f5a4d4da793414e848de627c6
  6. Affected versionversion=a6088845c2bf754d6cb2572b484180680b037804 <efed9a3337e341bd0989161b97453b52567bc59d

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.18; version=a6088845c2bf754d6cb2572b484180680b037804 <0b6b4b90b74c27bea968c214d820ba4254b903a5; version=a6088845c2bf754d6cb2572b484180680b037804 <2ef3c76540c49167a0bc3d5f80d00fd1fc4586df; version=a6088845c2bf754d6cb2572b484180680b037804 <54dbe2d2c1fcabf650c7a8b747601da355cd7f9f; version=a6088845c2bf754d6cb2572b484180680b037804 <a287cd84e047045f5a4d4da793414e848de627c6; version=a6088845c2bf754d6cb2572b484180680b037804 <efed9a3337e341bd0989161b97453b52567bc59d

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

CWE-129Improper Validation of Array Index
T1499.004Application or System Exploitation
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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