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CVE Record

CVE-2021-47255: kvm: LAPIC: Restore guard to prevent illegal APIC register access

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.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This Linux kernel KVM issue could let improper virtual APIC register access leak kernel stack contents. Business urgency depends on whether affected Linux kernels run KVM virtualization, especially with untrusted guests. The source bundle gives no CVSS score and no evidence of active exploitation.

Executive priority

Treat as a targeted virtualization host risk. Prioritize patch validation on KVM infrastructure before general-purpose Linux systems, because the cited impact is kernel stack information leakage in KVM LAPIC handling.

Technical view

CVE-2021-47255 restores a KVM LAPIC guard preventing APIC register accesses that touch bytes 4 through 15. The source says Intel SDM treats these accesses as undefined and that kvm_lapic_reg_read could leak kernel stack contents when the guard was missing.

Likely exposure

Exposure is most relevant to Linux hosts using KVM. The bundle lists affected Linux kernel versions and stable kernel fix commits, but it does not provide distribution-specific package names or backport status.

Exploitation context

CISA KEV status is false in the bundle, and no cited source states active exploitation. The bundle does not describe required attacker privileges, exploit maturity, or remote reachability, so exploitation context is incomplete.

Researcher notes

The key technical point is the restored bounds guard for APIC register reads. Avoid assuming exploitability beyond the source: it confirms possible stack content leakage but does not provide CVSS, CWE, prerequisites, or proof of exploitation.

Mitigation direction

  • Apply vendor-supported Linux kernel updates containing the referenced KVM LAPIC fix.
  • Check distribution advisories for backported fixes matching CVE-2021-47255.
  • Prioritize KVM hosts running untrusted or multi-tenant guest workloads.
  • If patch timing is constrained, review vendor guidance for operational mitigations.

Validation and detection

  • Inventory Linux hosts with KVM enabled or virtualization workloads present.
  • Compare running kernel versions against vendor advisories for CVE-2021-47255.
  • Confirm the relevant stable fix commit or backport is present.
  • Document any unpatched KVM hosts and guest trust boundaries.
Prepared
Confidence
medium
Sources
6

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2021-47255 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
5Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinux01402cf81051f796dac7c60ca11d6147153ca46a, 01402cf81051f796dac7c60ca11d6147153ca46a, 01402cf81051f796dac7c60ca11d6147153ca46a, 01402cf81051f796dac7c60ca11d6147153ca46aunaffected
LinuxLinux5.3, 0, 5.4.128, 5.10.46, 5.12.13, 5.13affected
Weakness

CWE details

No CWE listed

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