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Full vulnerability report · 2025
CVE-2021-47646High confidence

Revert "Revert "block, bfq: honor already-setup queue merges""

Linux · Linux

7.8HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

1 package state
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Ubuntu releaseSource packageVendor stateFixed versionEvidence
Ubuntu 24.04 LTSnoble · standard archivelinux-raspi-realtimeAffected, no fix publishedCanonical OVAL identifies this running kernel flavour as affected and does not publish a fixed package version in this definition.Not published in this feedCanonical record ↗Source updated 10 Sept 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2021-47646 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitykernel: Revert "Revert "block, bfq: honor already-setup queue merges""
70 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • bpftool as a component of Red Hat Enterprise Linux 8
  • kernel as a component of Red Hat Enterprise Linux 8
  • kernel-abi-stablelists as a component of Red Hat Enterprise Linux 8
  • kernel-abi-whitelists as a component of Red Hat Enterprise Linux 8
  • kernel-core as a component of Red Hat Enterprise Linux 8
  • kernel-cross-headers as a component of Red Hat Enterprise Linux 8
  • kernel-debug as a component of Red Hat Enterprise Linux 8
  • kernel-debug-core as a component of Red Hat Enterprise Linux 8
  • kernel-debug-devel as a component of Red Hat Enterprise Linux 8
  • kernel-debug-modules as a component of Red Hat Enterprise Linux 8
  • kernel-debug-modules-extra as a component of Red Hat Enterprise Linux 8
  • kernel-debug-modules-internal as a component of Red Hat Enterprise Linux 8
Summary
A flaw was found in the Linux kernel's Block Layer BFQ I/O scheduler. A Use-After-Free (UAF) vulnerability could be triggered by a specific commit related to queue merges. This flaw could lead to a system crash, resulting in a Denial of Service (DoS).
Remediation
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 The system must be rebooted for this update to take effect.
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2021-34659

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

In the Linux kernel, the following vulnerability has been resolved: Revert "Revert "block, bfq: honor already-setup queue merges"" A crash [1] happened to be triggered in conjunction with commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq: honor already-setup queue merges""). Yet, the reverted commit was not the one introducing the bug. In fact, it actually triggered a UAF introduced by a different commit, and now fixed by commit d29bd41428cf ("block, bfq: reset last_bfqq_created on group change"). So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges") out. This commit restores it. [1] https://bugzilla.kernel.org/show_bug.cgi?id=214503

What

In the Linux kernel, the following vulnerability has been resolved: Revert "Revert "block, bfq: honor already-setup queue merges"" A crash [1] happened to be triggered in conjunction with commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq: honor already-setup queue merges""). Yet, the reverted commit was not the one introducing the bug. In fact, it actually triggered a UAF introduced by a different commit, and now fixed by commit d29bd41428cf ("block, bfq: reset last_bfqq_created on group change"). So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges") out. This commit restores it. [1] https://bugzilla.kernel.org/show_bug.cgi?id=214503

Why

The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

What

In the Linux kernel, the following vulnerability has been resolved: Revert "Revert "block, bfq: honor already-setup queue merges"" A crash [1] happened to be triggered in conjunction with commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges"). The latter was then reverted by commit ebc69e897e17 ("Revert "block, bfq: honor already-setup queue merges""). Yet, the reverted commit was not the one introducing the bug. In fact, it actually triggered a UAF introduced by a different commit, and now fixed by commit d29bd41428cf ("block, bfq: reset last_bfqq_created on group change"). So, there is no point in keeping commit 2d52c58b9c9b ("block, bfq: honor already-setup queue merges") out. This commit restores it. [1] https://bugzilla.kernel.org/show_bug.cgi?id=214503

Why

The program can continue using memory after it has been released, producing unsafe and attacker-influenceable behaviour.

How

An attacker operating through local access may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
local access → Use After Free → disrupt the affected service
Attack surface
Local
Privileges required
Low: a basic authenticated account is required
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-416 ↗

CWE-416: Use After Free. The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVLocalAttack vector: The attacker needs local access to the vulnerable system.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
The issue can support a local privilege or sandbox boundary transition; normal system utilities may then be available in the gained context.
Denial of serviceCWE-416
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

CERT-FR · French · CERTFR-2025-AVI-0336Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47636 Référence CVE CVE-2021-47637 https://www.cve.org/CVERecord?id=CVE-2021-47637 Référence CVE CVE-2021-47638 https://www.cve.org/CVERecord?id=CVE-2021-47638 Référence CVE CVE-2021-47639 https://www.cve.org/CVERecord?id=CVE-2021-47639 Référence CVE CVE-2021-47641 https://www.cve.org/CVERecord?id=CVE-2021-47641 Référence CVE CVE-2021-47642 https://www.cve.org/CVERecord?id=CVE-2021-47642 Référence CVE CVE-2021-47643 https://www.cve.org/CVERecord?id=CVE-2021-47643 Référence CVE CVE-2021-47644 https://www.cve.org/CVERecord?id=CVE-2021-47644 Référence CVE CVE-2021-47645 https://www.cve.org/CVERecord?id=CVE-2021-47645 Référence CVE CVE-2021-47646 https://www.cve.org/CVERecord?id=CVE-2021-47646 Référence CVE CVE-2021-47647 https://www.cve.org/CVERecord?id=CVE-2021-47647 Référence CVE CVE-2021-47648 https://www.cve.org/CVERecord?id=CVE-2021-47648 Référence CVE CVE-2021-47649 https://www.cve.org/CVERecord?id=CVE-2021-47649 Référence CVE CVE-2021-47650 https://www.cve.org/CVERecord?id=CVE-2021-47650 Référence CVE CVE-2021-47651 https://www.cve.org/CVERecord?id=CVE-2021-47651 Référence CVE CVE-2021-47652 https://www.cve.org/CVERecord?id=CVE-2021-47652 Référence CVE CVE-2021-47653 https://www.cve.org/CVERecord?id=CVE-2021-47653 Référence CVE CVE-2021-47654 https://www.cve.org/CVERecord?id=

Official advisory
CERT-FR · French · CERTFR-2025-AVI-0307Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47636 Référence CVE CVE-2021-47637 https://www.cve.org/CVERecord?id=CVE-2021-47637 Référence CVE CVE-2021-47638 https://www.cve.org/CVERecord?id=CVE-2021-47638 Référence CVE CVE-2021-47639 https://www.cve.org/CVERecord?id=CVE-2021-47639 Référence CVE CVE-2021-47641 https://www.cve.org/CVERecord?id=CVE-2021-47641 Référence CVE CVE-2021-47642 https://www.cve.org/CVERecord?id=CVE-2021-47642 Référence CVE CVE-2021-47643 https://www.cve.org/CVERecord?id=CVE-2021-47643 Référence CVE CVE-2021-47644 https://www.cve.org/CVERecord?id=CVE-2021-47644 Référence CVE CVE-2021-47645 https://www.cve.org/CVERecord?id=CVE-2021-47645 Référence CVE CVE-2021-47646 https://www.cve.org/CVERecord?id=CVE-2021-47646 Référence CVE CVE-2021-47647 https://www.cve.org/CVERecord?id=CVE-2021-47647 Référence CVE CVE-2021-47648 https://www.cve.org/CVERecord?id=CVE-2021-47648 Référence CVE CVE-2021-47649 https://www.cve.org/CVERecord?id=CVE-2021-47649 Référence CVE CVE-2021-47650 https://www.cve.org/CVERecord?id=CVE-2021-47650 Référence CVE CVE-2021-47651 https://www.cve.org/CVERecord?id=CVE-2021-47651 Référence CVE CVE-2021-47652 https://www.cve.org/CVERecord?id=CVE-2021-47652 Référence CVE CVE-2021-47653 https://www.cve.org/CVERecord?id=CVE-2021-47653 Référence CVE CVE-2021-47654 https://www.cve.org/CVERecord?id=

Official advisory
CERT-FR · French · CERTFR-2025-AVI-0252Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47636 Référence CVE CVE-2021-47637 https://www.cve.org/CVERecord?id=CVE-2021-47637 Référence CVE CVE-2021-47638 https://www.cve.org/CVERecord?id=CVE-2021-47638 Référence CVE CVE-2021-47639 https://www.cve.org/CVERecord?id=CVE-2021-47639 Référence CVE CVE-2021-47641 https://www.cve.org/CVERecord?id=CVE-2021-47641 Référence CVE CVE-2021-47642 https://www.cve.org/CVERecord?id=CVE-2021-47642 Référence CVE CVE-2021-47643 https://www.cve.org/CVERecord?id=CVE-2021-47643 Référence CVE CVE-2021-47644 https://www.cve.org/CVERecord?id=CVE-2021-47644 Référence CVE CVE-2021-47645 https://www.cve.org/CVERecord?id=CVE-2021-47645 Référence CVE CVE-2021-47646 https://www.cve.org/CVERecord?id=CVE-2021-47646 Référence CVE CVE-2021-47647 https://www.cve.org/CVERecord?id=CVE-2021-47647 Référence CVE CVE-2021-47648 https://www.cve.org/CVERecord?id=CVE-2021-47648 Référence CVE CVE-2021-47649 https://www.cve.org/CVERecord?id=CVE-2021-47649 Référence CVE CVE-2021-47650 https://www.cve.org/CVERecord?id=CVE-2021-47650 Référence CVE CVE-2021-47651 https://www.cve.org/CVERecord?id=CVE-2021-47651 Référence CVE CVE-2021-47652 https://www.cve.org/CVERecord?id=CVE-2021-47652 Référence CVE CVE-2021-47653 https://www.cve.org/CVERecord?id=CVE-2021-47653 Référence CVE CVE-2021-47654 https://www.cve.org/CVERecord?id=

Official advisory
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
bpftool as a component of Red Hat Enterprise Linux 8; kernel as a component of Red Hat Enterprise Linux 8; kernel-abi-stablelists as a component of Red Hat Enterprise Linux 8; kernel-abi-whitelists as a component of Red Hat Enterprise Linux 8; kernel-core as a component of Red Hat Enterprise Linux 8; kernel-cross-headers as a component of Red Hat Enterprise Linux 8; kernel-debug as a component of Red Hat Enterprise Linux 8; kernel-debug-core as a component of Red Hat Enterprise Linux 8; kernel-debug-devel as a component of Red Hat Enterprise Linux 8; kernel-debug-modules as a component of Red Hat Enterprise Linux 8; kernel-debug-modules-extra as a component of Red Hat Enterprise Linux 8; kernel-debug-modules-internal as a component of Red Hat Enterprise Linux 8; kernel-devel as a component of Red Hat Enterprise Linux 8; kernel-doc as a component of Red Hat Enterprise Linux 8; kernel-headers as a component of Red Hat Enterprise Linux 8; kernel-ipaclones-internal as a component of Red Hat Enterprise Linux 8; kernel-modules as a component of Red Hat Enterprise Linux 8; kernel-modules-extra as a component of Red Hat Enterprise Linux 8; kernel-modules-internal as a component of Red Hat Enterprise Linux 8; kernel-rt as a component of Red Hat Enterprise Linux 8; kernel-rt-core as a component of Red Hat Enterprise Linux 8; kernel-rt-debug as a component of Red Hat Enterprise Linux 8; kernel-rt-debug-core as a component of Red Hat Enterprise Linux 8; kernel-rt-debug-devel as a component of Red Hat Enterprise Linux 8; kernel-rt-debug-kvm as a component of Red Hat Enterprise Linux 8; kernel-rt-debug-modules as a component of Red Hat Enterprise Linux 8; kernel-rt-debug-modules-extra as a component of Red Hat Enterprise Linux 8; kernel-rt-debug-modules-internal as a component of Red Hat Enterprise Linux 8; kernel-rt-devel as a component of Red Hat Enterprise Linux 8; kernel-rt-kvm as a component of Red Hat Enterprise Linux 8; and 40 more
Fixed
bpftool-debuginfo-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); bpftool-debuginfo-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); bpftool-debuginfo-0:5.14.0-162.6.1.el9_1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9); bpftool-debuginfo-0:5.14.0-162.6.1.el9_1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-debuginfo-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-debuginfo-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-debuginfo-0:5.14.0-162.6.1.el9_1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-debuginfo-0:5.14.0-162.6.1.el9_1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-0:5.14.0-162.6.1.el9_1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-0:5.14.0-162.6.1.el9_1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-matched-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-matched-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-matched-0:5.14.0-162.6.1.el9_1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debug-devel-matched-0:5.14.0-162.6.1.el9_1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-0:5.14.0-162.6.1.el9_1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-0:5.14.0-162.6.1.el9_1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-common-aarch64-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-common-ppc64le-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-common-s390x-0:5.14.0-162.6.1.el9_1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-debuginfo-common-x86_64-0:5.14.0-162.6.1.el9_1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-devel-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-devel-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-devel-0:5.14.0-162.6.1.el9_1.s390x as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-devel-0:5.14.0-162.6.1.el9_1.x86_64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-devel-matched-0:5.14.0-162.6.1.el9_1.aarch64 as a component of Red Hat Enterprise Linux AppStream (v. 9); kernel-devel-matched-0:5.14.0-162.6.1.el9_1.ppc64le as a component of Red Hat Enterprise Linux AppStream (v. 9); and 136 more
Action
For details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 The system must be rebooted for this update to take effect.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 26 Feb 2025 · Last source change 11 Aug 2026, 02:05 UTC · CWE-416 · Use After Free

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2021-34659
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCISA ADP
NVD statusNVD modified after enrichment

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release or patch reference recorded
ENISA EUVD · EUVD-2021-34659↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Patch or update reference↗Patch or update reference↗Patch or update reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2021-47646 · cve.blacktree.nl