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Full vulnerability report · 2024
CVE-2021-47255High confidence

kvm: LAPIC: Restore guard to prevent illegal APIC register access

Linux · Linux

7.1HighCVSS 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 11 Sept 2026
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-2021-33903

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: kvm: LAPIC: Restore guard to prevent illegal APIC register access Per the SDM, "any access that touches bytes 4 through 15 of an APIC register may cause undefined behavior and must not be executed." Worse, such an access in kvm_lapic_reg_read can result in a leak of kernel stack contents. Prior to commit 01402cf81051 ("kvm: LAPIC: write down valid APIC registers"), such an access was explicitly disallowed. Restore the guard that was removed in that commit.

What

In the Linux kernel, the following vulnerability has been resolved: kvm: LAPIC: Restore guard to prevent illegal APIC register access Per the SDM, "any access that touches bytes 4 through 15 of an APIC register may cause undefined behavior and must not be executed." Worse, such an access in kvm_lapic_reg_read can result in a leak of kernel stack contents. Prior to commit 01402cf81051 ("kvm: LAPIC: write down valid APIC registers"), such an access was explicitly disallowed. Restore the guard that was removed in that commit.

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 cause the confidentiality, integrity or availability impact described by the vendor.

What

In the Linux kernel, the following vulnerability has been resolved: kvm: LAPIC: Restore guard to prevent illegal APIC register access Per the SDM, "any access that touches bytes 4 through 15 of an APIC register may cause undefined behavior and must not be executed." Worse, such an access in kvm_lapic_reg_read can result in a leak of kernel stack contents. Prior to commit 01402cf81051 ("kvm: LAPIC: write down valid APIC registers"), such an access was explicitly disallowed. Restore the guard that was removed in that commit.

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 cause the confidentiality, integrity or availability impact described by the vendor.

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 → cause the confidentiality, integrity or availability impact described by the vendor
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:N/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.INoneIntegrity impact: No direct loss is represented by this metric.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.
A

Official authority intelligence

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

Cyber Security Agency of Singapore · English · CSA-SB-20240522Security Bulletin 22 May 2024

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 22 May 2024, published on 22 May 2024. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
CERT-FR · French · CERTFR-2025-AVI-0529Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47170 Référence CVE CVE-2021-47220 https://www.cve.org/CVERecord?id=CVE-2021-47220 Référence CVE CVE-2021-47229 https://www.cve.org/CVERecord?id=CVE-2021-47229 Référence CVE CVE-2021-47231 https://www.cve.org/CVERecord?id=CVE-2021-47231 Référence CVE CVE-2021-47236 https://www.cve.org/CVERecord?id=CVE-2021-47236 Référence CVE CVE-2021-47239 https://www.cve.org/CVERecord?id=CVE-2021-47239 Référence CVE CVE-2021-47240 https://www.cve.org/CVERecord?id=CVE-2021-47240 Référence CVE CVE-2021-47246 https://www.cve.org/CVERecord?id=CVE-2021-47246 Référence CVE CVE-2021-47252 https://www.cve.org/CVERecord?id=CVE-2021-47252 Référence CVE CVE-2021-47255 https://www.cve.org/CVERecord?id=CVE-2021-47255 Référence CVE CVE-2021-47260 https://www.cve.org/CVERecord?id=CVE-2021-47260 Référence CVE CVE-2021-47288 https://www.cve.org/CVERecord?id=CVE-2021-47288 Référence CVE CVE-2021-47296 https://www.cve.org/CVERecord?id=CVE-2021-47296 Référence CVE CVE-2021-47314 https://www.cve.org/CVERecord?id=CVE-2021-47314 Référence CVE CVE-2021-47315 https://www.cve.org/CVERecord?id=CVE-2021-47315 Référence CVE CVE-2021-47485 https://www.cve.org/CVERecord?id=CVE-2021-47485 Référence CVE CVE-2021-47500 https://www.cve.org/CVERecord?id=CVE-2021-47500 Référence CVE CVE-2021-47511 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0526Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47241 Référence CVE CVE-2021-47245 https://www.cve.org/CVERecord?id=CVE-2021-47245 Référence CVE CVE-2021-47246 https://www.cve.org/CVERecord?id=CVE-2021-47246 Référence CVE CVE-2021-47248 https://www.cve.org/CVERecord?id=CVE-2021-47248 Référence CVE CVE-2021-47249 https://www.cve.org/CVERecord?id=CVE-2021-47249 Référence CVE CVE-2021-47250 https://www.cve.org/CVERecord?id=CVE-2021-47250 Référence CVE CVE-2021-47252 https://www.cve.org/CVERecord?id=CVE-2021-47252 Référence CVE CVE-2021-47253 https://www.cve.org/CVERecord?id=CVE-2021-47253 Référence CVE CVE-2021-47254 https://www.cve.org/CVERecord?id=CVE-2021-47254 Référence CVE CVE-2021-47255 https://www.cve.org/CVERecord?id=CVE-2021-47255 Référence CVE CVE-2021-47258 https://www.cve.org/CVERecord?id=CVE-2021-47258 Référence CVE CVE-2021-47259 https://www.cve.org/CVERecord?id=CVE-2021-47259 Référence CVE CVE-2021-47260 https://www.cve.org/CVERecord?id=CVE-2021-47260 Référence CVE CVE-2021-47261 https://www.cve.org/CVERecord?id=CVE-2021-47261 Référence CVE CVE-2021-47263 https://www.cve.org/CVERecord?id=CVE-2021-47263 Référence CVE CVE-2021-47265 https://www.cve.org/CVERecord?id=CVE-2021-47265 Référence CVE CVE-2021-47267 https://www.cve.org/CVERecord?id=CVE-2021-47267 Référence CVE CVE-2021-47269 https://www.cve.org/CVERecord?id=

Official advisory ↗
CERT-FR · French · CERTFR-2024-AVI-0496Multiples vulnérabilités dans le noyau Linux de SUSE

d?id=CVE-2021-47241 Référence CVE CVE-2021-47245 https://www.cve.org/CVERecord?id=CVE-2021-47245 Référence CVE CVE-2021-47246 https://www.cve.org/CVERecord?id=CVE-2021-47246 Référence CVE CVE-2021-47248 https://www.cve.org/CVERecord?id=CVE-2021-47248 Référence CVE CVE-2021-47249 https://www.cve.org/CVERecord?id=CVE-2021-47249 Référence CVE CVE-2021-47250 https://www.cve.org/CVERecord?id=CVE-2021-47250 Référence CVE CVE-2021-47252 https://www.cve.org/CVERecord?id=CVE-2021-47252 Référence CVE CVE-2021-47253 https://www.cve.org/CVERecord?id=CVE-2021-47253 Référence CVE CVE-2021-47254 https://www.cve.org/CVERecord?id=CVE-2021-47254 Référence CVE CVE-2021-47255 https://www.cve.org/CVERecord?id=CVE-2021-47255 Référence CVE CVE-2021-47258 https://www.cve.org/CVERecord?id=CVE-2021-47258 Référence CVE CVE-2021-47259 https://www.cve.org/CVERecord?id=CVE-2021-47259 Référence CVE CVE-2021-47260 https://www.cve.org/CVERecord?id=CVE-2021-47260 Référence CVE CVE-2021-47261 https://www.cve.org/CVERecord?id=CVE-2021-47261 Référence CVE CVE-2021-47263 https://www.cve.org/CVERecord?id=CVE-2021-47263 Référence CVE CVE-2021-47265 https://www.cve.org/CVERecord?id=CVE-2021-47265 Référence CVE CVE-2021-47267 https://www.cve.org/CVERecord?id=CVE-2021-47267 Référence CVE CVE-2021-47269 https://www.cve.org/CVERecord?id=

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2021-021832Linux 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.
Patch available
Affected
Linux: 01402cf81051f796dac7c60ca11d6147153ca46a < bf99ea52970caeb4583bdba1192c1f9b53b12c84, 01402cf81051f796dac7c60ca11d6147153ca46a < 018685461a5b9a9a70e664ac77aef0d7415a3fd5, 01402cf81051f796dac7c60ca11d6147153ca46a < a2aff09807fbe4018c269d3773a629949058b210, 01402cf81051f796dac7c60ca11d6147153ca46a < 218bf772bddd221489c38dde6ef8e917131161f6, 5.3
Fixed
Linux: < 5.3, 5.4.128 ≤ 5.4.*, 5.10.46 ≤ 5.10.*, 5.12.13 ≤ 5.12.*, 5.13 ≤ *
Action
Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
Workaround
No verified workaround is recorded. Limit untrusted access and use least privilege until authoritative guidance is available.
04

Evidence and provenance

Published 21 May 2024 · Last source change 11 May 2026, 13:50 UTC · CWE not yet assigned

CVE recordCVE.org · 5.2
CVSS sourceNIST NVD
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-2021-33903
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceUnavailable
NVD statusNVD enriched

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
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-2021-47255 · cve.blacktree.nl