CVE-2021-47255

Kernel stack disclosure via illegal LAPIC read

Published May 21, 2024 · Updated May 11, 2026

Information disclosure in Linux kernel KVM allows local users to read host kernel stack contents through an illegal LAPIC register access. The kvm_lapic_reg_read path fails to reject offsets touching bytes 4 through 15 of an APIC register and returns adjacent stack data. Reaching the flaw requires local low-privileged access to an x86 KVM virtual machine; the bounded consequence is host kernel-memory disclosure, and illegal accesses also have undefined behavior.

CVSS severity7.1
High
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Linux kernel KVM allows local users to read host kernel stack contents through an illegal LAPIC register access. The kvm_lapic_reg_read path fails to reject offsets touching bytes 4 through 15 of an APIC register and returns adjacent stack data. Reaching the flaw requires local low-privileged access to an x86 KVM virtual machine; the bounded consequence is host kernel-memory disclosure, and illegal accesses also have undefined behavior.

The record

CVE
CVE-2021-47255
Published
May 21, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1005
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 21, 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=01402cf81051f796dac7c60ca11d6147153ca46a <018685461a5b9a9a70e664ac77aef0d7415a3fd5
  2. Affected versionversion=01402cf81051f796dac7c60ca11d6147153ca46a <218bf772bddd221489c38dde6ef8e917131161f6
  3. Affected versionversion=01402cf81051f796dac7c60ca11d6147153ca46a <a2aff09807fbe4018c269d3773a629949058b210
  4. Affected versionversion=01402cf81051f796dac7c60ca11d6147153ca46a <bf99ea52970caeb4583bdba1192c1f9b53b12c84
  5. Affected versionversion=5.3

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=01402cf81051f796dac7c60ca11d6147153ca46a <018685461a5b9a9a70e664ac77aef0d7415a3fd5; version=01402cf81051f796dac7c60ca11d6147153ca46a <218bf772bddd221489c38dde6ef8e917131161f6; version=01402cf81051f796dac7c60ca11d6147153ca46a <a2aff09807fbe4018c269d3773a629949058b210; version=01402cf81051f796dac7c60ca11d6147153ca46a <bf99ea52970caeb4583bdba1192c1f9b53b12c84; version=5.3

Published CVSS scores

7.1NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1005Data from Local System

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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