LiveActive security incident?Get immediate response
CVE Record

CVE-2021-47008: KVM: SVM: Make sure GHCB is mapped before updating

In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Make sure GHCB is mapped before updating Access to the GHCB is mainly in the VMGEXIT path and it is known that the GHCB will be mapped. But there are two paths where it is possible the GHCB might not be mapped. The sev_vcpu_deliver_sipi_vector() routine will update the GHCB to inform the caller of the AP Reset Hold NAE event that a SIPI has been delivered. However, if a SIPI is performed without a corresponding AP Reset Hold, then the GHCB might not be mapped (depending on the previous VMEXIT), which will result in a NULL pointer dereference. The svm_complete_emulated_msr() routine will update the GHCB to inform the caller of a RDMSR/WRMSR operation about any errors. While it is likely that the GHCB will be mapped in this situation, add a safe guard in this path to be certain a NULL pointer dereference is not encountered.

UnknownCVSS not scoredNot KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

This is a Linux kernel KVM issue in AMD SVM/SEV handling. In two uncommon paths, the kernel may update the guest-host communication block before it is mapped, causing a NULL pointer dereference. The public record does not provide CVSS, CWE, or confirmed exploitation. Treat it mainly as a virtualization host stability concern until vendor guidance says otherwise.

Executive priority

Prioritize as a virtualization platform maintenance item, not an emergency based on current evidence. Patch affected KVM hosts during the next risk-based maintenance window, sooner where untrusted tenant guests share AMD SVM/SEV infrastructure.

Technical view

KVM SVM code assumed the GHCB was mapped when sev_vcpu_deliver_sipi_vector() and svm_complete_emulated_msr() updated it. A SIPI without matching AP Reset Hold, or an emulated MSR completion path, could leave GHCB unmapped and trigger a NULL dereference. Stable commits add mapping checks before GHCB updates.

Likely exposure

Exposure appears limited to Linux systems using KVM on AMD SVM/SEV-capable virtualization hosts in affected kernel lines. The source bundle lists Linux 5.11, 5.11.22, 5.12.5, and 5.13 as affected, but does not provide distribution-specific package status.

Exploitation context

The provided sources do not show active exploitation, public exploit availability, or KEV listing. The described failure is a kernel NULL pointer dereference reachable through specific KVM SVM/SEV GHCB update paths, so practical risk depends on whether untrusted guests can trigger those paths.

Researcher notes

Evidence is limited to the CVE record and kernel stable references. No CVSS, CWE, exploit status, or distribution matrix is included. Focus validation on affected kernel lineage, AMD KVM SVM/SEV usage, and whether the stable GHCB mapping safeguards are present.

Mitigation direction

  • Check your Linux vendor advisory and kernel package status for CVE-2021-47008.
  • Upgrade affected KVM virtualization hosts to a kernel containing the referenced stable fixes.
  • Prioritize hosts running AMD SVM/SEV workloads or untrusted guest tenants.
  • If patch timing is unclear, reduce exposure of untrusted guests on affected hosts.

Validation and detection

  • Inventory Linux kernel versions on KVM hosts, especially AMD SVM/SEV systems.
  • Confirm whether vendor kernel builds include the referenced stable commits.
  • Review crash logs for KVM SVM, GHCB, or NULL pointer dereference messages.
  • Verify post-update kernel version and rerun standard virtualization health checks.
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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cve · low confidence lookup

CVE-2021-47008 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
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

CVECVE Program Container
CISA-ADPCISA ADP Vulnrichment
other:ssvc

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxf1c6366e304328de301be362eca905a3503ff33b, f1c6366e304328de301be362eca905a3503ff33b, f1c6366e304328de301be362eca905a3503ff33bunaffected
LinuxLinux5.11, 0, 5.11.22, 5.12.5, 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.