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CVE Record

CVE-2021-47062: KVM: SVM: Use online_vcpus, not created_vcpus, to iterate over vCPUs

In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Use online_vcpus, not created_vcpus, to iterate over vCPUs Use the kvm_for_each_vcpu() helper to iterate over vCPUs when encrypting VMSAs for SEV, which effectively switches to use online_vcpus instead of created_vcpus. This fixes a possible null-pointer dereference as created_vcpus does not guarantee a vCPU exists, since it is updated at the very beginning of KVM_CREATE_VCPU. created_vcpus exists to allow the bulk of vCPU creation to run in parallel, while still correctly restricting the max number of max vCPUs.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel KVM issue in the SVM/SEV virtualization path. Under a specific vCPU creation race, the kernel could dereference a null pointer. The public record does not provide CVSS, confirmed impact scope, or exploitation evidence, so urgency depends on whether affected virtualization hosts are in use.

Executive priority

Treat as a targeted infrastructure hygiene issue, not an emergency from current evidence. Prioritize patching affected virtualization hosts, especially where KVM SVM/SEV is used, while watching vendor advisories for severity updates.

Technical view

KVM SVM code used created_vcpus while encrypting VMSAs for SEV. Because created_vcpus is incremented early in KVM_CREATE_VCPU, iteration could observe a slot where no vCPU object exists, causing a possible null-pointer dereference. The fix switches iteration to kvm_for_each_vcpu(), using online_vcpus semantics.

Likely exposure

Exposure is most likely on Linux systems running affected kernel versions with KVM SVM/SEV functionality. The bundle lists Linux 5.11, 5.11.21, 5.12.4, and 5.13 as affected indicators, but does not provide distribution package mappings.

Exploitation context

The source bundle does not show CISA KEV listing, public exploitation, exploit maturity, or attacker prerequisites. It only describes a possible null-pointer dereference fixed in Linux stable commits.

Researcher notes

Evidence is limited to the CVE description and Linux stable commit references. No CWE, CVSS, exploit status, or vendor package matrix is included. Analysis should focus on kernel version lineage and whether the relevant KVM SVM/SEV code path is reachable.

Mitigation direction

  • Identify Linux KVM hosts running affected kernel versions.
  • Prioritize hosts using SVM or SEV virtualization paths.
  • Apply vendor kernel updates containing the referenced stable fixes.
  • If updates are delayed, check vendor guidance for supported temporary controls.
  • Track distribution advisories for exact fixed package versions.

Validation and detection

  • Inventory kernel versions across virtualization hosts.
  • Confirm whether KVM SVM or SEV features are enabled or used.
  • Verify installed kernel includes one referenced stable fix commit.
  • Review host logs for unexplained KVM-related null dereference crashes.
  • Document affected and remediated hosts for audit tracking.
Prepared
Confidence
medium
Sources
5

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

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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CVE-2021-47062 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
4Source 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
LinuxLinuxad73109ae7ec30d5bfb76be108e304f9f0af4829, ad73109ae7ec30d5bfb76be108e304f9f0af4829, ad73109ae7ec30d5bfb76be108e304f9f0af4829unaffected
LinuxLinux5.11, 0, 5.11.21, 5.12.4, 5.13affected
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.