BlackTreeCVE Intelligence
← Back to the CVE catalogue
Full vulnerability report · 2024
CVE-2021-47189High confidence

btrfs: fix memory ordering between normal and ordered work functions

Linux · Linux

7.8HighCVSS 3.1
Recommended action
Patch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 43 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityHighOperational priority:Medium, lowered one band.downgradedsince 5 Aug 2026

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • Exploitation requires an existing local or physical foothold with privileges.
  • EPSS is 0.67% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict local access and enforce least privilege on affected hosts.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Linux Linux and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Cross-source reconciliation

Remediation availability differs by product scope

Verified remediation exists for at least one product or source, but 43 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Distribution package intelligence

Release-specific package status

Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

5 package states
Package result overrides the generic status

BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 1 affected package state shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.

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.

Distribution releaseSource packageVendor stateFixed versionEvidence
Debian trixietrixie · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.5-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian bookwormbookworm · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.5-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian forkyforky · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.5-1Debian Security Tracker ↗Source updated 5 Oct 2026
Debian sidsid · sourcelinuxVendor fix publishedDebian records a fixed source-package version for this release.5.15.5-1Debian Security Tracker ↗Source updated 5 Oct 2026
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 Ubuntu Security ↗Source updated 5 Oct 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-2021-47189 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitykernel: btrfs: fix memory ordering between normal and ordered work functions
42 known affected

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

  • kernel as a component of Red Hat Enterprise Linux 6
  • kernel-abi-whitelists as a component of Red Hat Enterprise Linux 6
  • kernel-bootwrapper as a component of Red Hat Enterprise Linux 6
  • kernel-debug as a component of Red Hat Enterprise Linux 6
  • kernel-debug-devel as a component of Red Hat Enterprise Linux 6
  • kernel-devel as a component of Red Hat Enterprise Linux 6
  • kernel-doc as a component of Red Hat Enterprise Linux 6
  • kernel-firmware as a component of Red Hat Enterprise Linux 6
  • kernel-headers as a component of Red Hat Enterprise Linux 6
  • kernel-kdump as a component of Red Hat Enterprise Linux 6
  • kernel-kdump-devel as a component of Red Hat Enterprise Linux 6
  • kernel.src as a component of Red Hat Enterprise Linux 6
Summary
A memory ordering flaw was found in the btrfs file system code in the Linux kernel, which could lead to unpredictable behavior or security risks. The vulnerability is due to improper synchronization between normal and ordered work functions.
Remediation
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
Optional official sources

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

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

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-2021-33837

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 actionPatch only the product branches with a verified fix

High technical severity; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 43 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.

Fix availability varies by product
01

What, why and how

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix memory ordering between normal and ordered work functions Ordered work functions aren't guaranteed to be handled by the same thread which executed the normal work functions. The only way execution between normal/ordered functions is synchronized is via the WORK_DONE_BIT, unfortunately the used bitops don't guarantee any ordering whatsoever. This manifested as seemingly inexplicable crashes on ARM64, where async_chunk::inode is seen as non-null in async_cow_submit which causes submit_compressed_extents to be called and crash occurs because async_chunk::inode suddenly became NULL. The call trace was similar to: pc : submit_compressed_extents+0x38/0x3d0 lr : async_cow_submit+0x50/0xd0 sp : ffff800015d4bc20 <registers omitted for brevity> Call trace: submit_compressed_extents+0x38/0x3d0 async_cow_submit+0x50/0xd0 run_ordered_work+0xc8/0x280 btrfs_work_helper+0x98/0x250 process_one_work+0x1f0/0x4ac worker_thread+0x188/0x504 kthread+0x110/0x114 ret_from_fork+0x10/0x18 Fix this by adding respective barrier calls which ensure that all accesses preceding setting of WORK_DONE_BIT are strictly ordered before setting the flag. At the same time add a read barrier after reading of WORK_DONE_BIT in run_ordered_work which ensures all subsequent loads would be strictly ordered after reading the bit. This in turn ensures are all accesses before WORK_DONE_BIT are going to be strictly ordered before any access that can occur in ordered_func.

What

In the Linux kernel, the following vulnerability has been resolved: btrfs: fix memory ordering between normal and ordered work functions Ordered work functions aren't guaranteed to be handled by the same thread which executed the normal work functions. The only way execution between normal/ordered functions is synchronized is via the WORK_DONE_BIT, unfortunately the used bitops don't guarantee any ordering whatsoever. This manifested as seemingly inexplicable crashes on ARM64, where async_chunk::inode is seen as non-null in async_cow_submit which causes submit_compressed_extents to be called and crash occurs because async_chunk::inode suddenly became NULL. The call trace was similar to: pc : submit_compressed_extents+0x38/0x3d0 lr : async_cow_submit+0x50/0xd0 sp : ffff800015d4bc20 <registers omitted for brevity> Call trace: submit_compressed_extents+0x38/0x3d0 async_cow_submit+0x50/0xd0 run_ordered_work+0xc8/0x280 btrfs_work_helper+0x98/0x250 process_one_work+0x1f0/0x4ac worker_thread+0x188/0x504 kthread+0x110/0x114 ret_from_fork+0x10/0x18 Fix this by adding respective barrier calls which ensure that all accesses preceding setting of WORK_DONE_BIT are strictly ordered before setting the flag. At the same time add a read barrier after reading of WORK_DONE_BIT in run_ordered_work which ensures all subsequent loads would be strictly ordered after reading the bit. This in turn ensures are all accesses before WORK_DONE_BIT are going to be strictly ordered before any access that can occur in ordered_func.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

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: btrfs: fix memory ordering between normal and ordered work functions Ordered work functions aren't guaranteed to be handled by the same thread which executed the normal work functions. The only way execution between normal/ordered functions is synchronized is via the WORK_DONE_BIT, unfortunately the used bitops don't guarantee any ordering whatsoever. This manifested as seemingly inexplicable crashes on ARM64, where async_chunk::inode is seen as non-null in async_cow_submit which causes submit_compressed_extents to be called and crash occurs because async_chunk::inode suddenly became NULL. The call trace was similar to: pc : submit_compressed_extents+0x38/0x3d0 lr : async_cow_submit+0x50/0xd0 sp : ffff800015d4bc20 <registers omitted for brevity> Call trace: submit_compressed_extents+0x38/0x3d0 async_cow_submit+0x50/0xd0 run_ordered_work+0xc8/0x280 btrfs_work_helper+0x98/0x250 process_one_work+0x1f0/0x4ac worker_thread+0x188/0x504 kthread+0x110/0x114 ret_from_fork+0x10/0x18 Fix this by adding respective barrier calls which ensure that all accesses preceding setting of WORK_DONE_BIT are strictly ordered before setting the flag. At the same time add a read barrier after reading of WORK_DONE_BIT in run_ordered_work which ensures all subsequent loads would be strictly ordered after reading the bit. This in turn ensures are all accesses before WORK_DONE_BIT are going to be strictly ordered before any access that can occur in ordered_func.

Why

The current structured CVE record identifies a security weakness, but the root cause requires confirmation in the linked vendor material.

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 → vulnerable operation → 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.
CWE not yet assigned
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 service
A

Official authority intelligence

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

BSI · German · WID-SEC-2024-0851Linux Kernel: Mehrere Schwachstellen

Ein lokaler Angreifer kann mehrere Schwachstellen im Linux Kernel ausnutzen, um einen Denial of Service Angriff durchzuführen oder unbekannte Auswirkungen zu verursachen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20240417Security Bulletin 17 Apr 2024

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 17 Apr 2024, published on 17 April 2024. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0458Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47177 Référence CVE CVE-2021-47179 https://www.cve.org/CVERecord?id=CVE-2021-47179 Référence CVE CVE-2021-47180 https://www.cve.org/CVERecord?id=CVE-2021-47180 Référence CVE CVE-2021-47181 https://www.cve.org/CVERecord?id=CVE-2021-47181 Référence CVE CVE-2021-47182 https://www.cve.org/CVERecord?id=CVE-2021-47182 Référence CVE CVE-2021-47183 https://www.cve.org/CVERecord?id=CVE-2021-47183 Référence CVE CVE-2021-47184 https://www.cve.org/CVERecord?id=CVE-2021-47184 Référence CVE CVE-2021-47185 https://www.cve.org/CVERecord?id=CVE-2021-47185 Référence CVE CVE-2021-47188 https://www.cve.org/CVERecord?id=CVE-2021-47188 Référence CVE CVE-2021-47189 https://www.cve.org/CVERecord?id=CVE-2021-47189 Référence CVE CVE-2021-47198 https://www.cve.org/CVERecord?id=CVE-2021-47198 Référence CVE CVE-2021-47202 https://www.cve.org/CVERecord?id=CVE-2021-47202 Référence CVE CVE-2021-47203 https://www.cve.org/CVERecord?id=CVE-2021-47203 Référence CVE CVE-2021-47204 https://www.cve.org/CVERecord?id=CVE-2021-47204 Référence CVE CVE-2021-47205 https://www.cve.org/CVERecord?id=CVE-2021-47205 Référence CVE CVE-2021-47207 https://www.cve.org/CVERecord?id=CVE-2021-47207 Référence CVE CVE-2021-47211 https://www.cve.org/CVERecord?id=CVE-2021-47211 Référence CVE CVE-2021-47216 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0440Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47177 Référence CVE CVE-2021-47179 https://www.cve.org/CVERecord?id=CVE-2021-47179 Référence CVE CVE-2021-47180 https://www.cve.org/CVERecord?id=CVE-2021-47180 Référence CVE CVE-2021-47181 https://www.cve.org/CVERecord?id=CVE-2021-47181 Référence CVE CVE-2021-47182 https://www.cve.org/CVERecord?id=CVE-2021-47182 Référence CVE CVE-2021-47183 https://www.cve.org/CVERecord?id=CVE-2021-47183 Référence CVE CVE-2021-47184 https://www.cve.org/CVERecord?id=CVE-2021-47184 Référence CVE CVE-2021-47185 https://www.cve.org/CVERecord?id=CVE-2021-47185 Référence CVE CVE-2021-47188 https://www.cve.org/CVERecord?id=CVE-2021-47188 Référence CVE CVE-2021-47189 https://www.cve.org/CVERecord?id=CVE-2021-47189 Référence CVE CVE-2021-47198 https://www.cve.org/CVERecord?id=CVE-2021-47198 Référence CVE CVE-2021-47202 https://www.cve.org/CVERecord?id=CVE-2021-47202 Référence CVE CVE-2021-47203 https://www.cve.org/CVERecord?id=CVE-2021-47203 Référence CVE CVE-2021-47204 https://www.cve.org/CVERecord?id=CVE-2021-47204 Référence CVE CVE-2021-47205 https://www.cve.org/CVERecord?id=CVE-2021-47205 Référence CVE CVE-2021-47207 https://www.cve.org/CVERecord?id=CVE-2021-47207 Référence CVE CVE-2021-47211 https://www.cve.org/CVERecord?id=CVE-2021-47211 Référence CVE CVE-2021-47216 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0420Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47179 Référence CVE CVE-2021-47180 https://www.cve.org/CVERecord?id=CVE-2021-47180 Référence CVE CVE-2021-47181 https://www.cve.org/CVERecord?id=CVE-2021-47181 Référence CVE CVE-2021-47182 https://www.cve.org/CVERecord?id=CVE-2021-47182 Référence CVE CVE-2021-47183 https://www.cve.org/CVERecord?id=CVE-2021-47183 Référence CVE CVE-2021-47184 https://www.cve.org/CVERecord?id=CVE-2021-47184 Référence CVE CVE-2021-47185 https://www.cve.org/CVERecord?id=CVE-2021-47185 Référence CVE CVE-2021-47187 https://www.cve.org/CVERecord?id=CVE-2021-47187 Référence CVE CVE-2021-47188 https://www.cve.org/CVERecord?id=CVE-2021-47188 Référence CVE CVE-2021-47189 https://www.cve.org/CVERecord?id=CVE-2021-47189 Référence CVE CVE-2021-47191 https://www.cve.org/CVERecord?id=CVE-2021-47191 Référence CVE CVE-2021-47192 https://www.cve.org/CVERecord?id=CVE-2021-47192 Référence CVE CVE-2021-47193 https://www.cve.org/CVERecord?id=CVE-2021-47193 Référence CVE CVE-2021-47194 https://www.cve.org/CVERecord?id=CVE-2021-47194 Référence CVE CVE-2021-47195 https://www.cve.org/CVERecord?id=CVE-2021-47195 Référence CVE CVE-2021-47196 https://www.cve.org/CVERecord?id=CVE-2021-47196 Référence CVE CVE-2021-47197 https://www.cve.org/CVERecord?id=CVE-2021-47197 Référence CVE CVE-2021-47198 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0363Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47175 Référence CVE CVE-2021-47176 https://www.cve.org/CVERecord?id=CVE-2021-47176 Référence CVE CVE-2021-47177 https://www.cve.org/CVERecord?id=CVE-2021-47177 Référence CVE CVE-2021-47179 https://www.cve.org/CVERecord?id=CVE-2021-47179 Référence CVE CVE-2021-47180 https://www.cve.org/CVERecord?id=CVE-2021-47180 Référence CVE CVE-2021-47181 https://www.cve.org/CVERecord?id=CVE-2021-47181 Référence CVE CVE-2021-47182 https://www.cve.org/CVERecord?id=CVE-2021-47182 Référence CVE CVE-2021-47183 https://www.cve.org/CVERecord?id=CVE-2021-47183 Référence CVE CVE-2021-47185 https://www.cve.org/CVERecord?id=CVE-2021-47185 Référence CVE CVE-2021-47189 https://www.cve.org/CVERecord?id=CVE-2021-47189 Référence CVE CVE-2021-47202 https://www.cve.org/CVERecord?id=CVE-2021-47202 Référence CVE CVE-2022-0487 https://www.cve.org/CVERecord?id=CVE-2022-0487 Référence CVE CVE-2022-4744 https://www.cve.org/CVERecord?id=CVE-2022-4744 Référence CVE CVE-2022-48626 https://www.cve.org/CVERecord?id=CVE-2022-48626 Référence CVE CVE-2022-48627 https://www.cve.org/CVERecord?id=CVE-2022-48627 Référence CVE CVE-2022-48628 https://www.cve.org/CVERecord?id=CVE-2022-48628 Référence CVE CVE-2022-48629 https://www.cve.org/CVERecord?id=CVE-2022-48629 Référence CVE CVE-2022-48630 https://www.cve.org/CVERecord?id=CVE-

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-021829Linux の Linux Kernel における脆弱性

Linux の Linux Kernel には、不特定の脆弱性が存在します。

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.
Fix availability varies by product
Affected
Fixed
Linux: < 3.15, 4.4.293 ≤ 4.4.*, 4.9.291 ≤ 4.9.*, 4.14.256 ≤ 4.14.*, 4.19.218 ≤ 4.19.*, 5.4.162 ≤ 5.4.*, 5.10.82 ≤ 5.10.*, 5.15.5 ≤ 5.15.*, 5.16 ≤ *
Action
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.
04

Evidence and provenance

Published 10 Apr 2024 · Last source change 5 Aug 2026, 08:46 UTC · CWE not yet assigned

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-2021-33837
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceUnavailable
NVD statusNVD modified after enrichment

Missing structured fields: CWE classification. Missing data is not evidence of low risk; review the primary advisory.

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-2021-33837↗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-2021-47189 · cve.blacktree.nl