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CVE Record

CVE-2026-43133: KVM: nSVM: Always use vmcb01 in VMLOAD/VMSAVE emulation

In the Linux kernel, the following vulnerability has been resolved: KVM: nSVM: Always use vmcb01 in VMLOAD/VMSAVE emulation Commit cc3ed80ae69f ("KVM: nSVM: always use vmcb01 to for vmsave/vmload of guest state") made KVM always use vmcb01 for the fields controlled by VMSAVE/VMLOAD, but it missed updating the VMLOAD/VMSAVE emulation code to always use vmcb01. As a result, if VMSAVE/VMLOAD is executed by an L2 guest and is not intercepted by L1, KVM will mistakenly use vmcb02. Always use vmcb01 instead of the current VMCB.

HighCVSS 7.9Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-43133 is a Linux KVM kernel flaw affecting nested AMD virtualization handling. A low-privileged local user in the relevant virtualization path could trigger incorrect virtual machine control state handling, with the strongest documented impact on availability.

Executive priority

Treat as high priority for virtualization infrastructure, especially platforms offering nested virtualization. The risk is narrower than internet-facing remote code execution, but availability impact on hypervisor-backed services can be business significant.

Technical view

In KVM nSVM, VMLOAD/VMSAVE emulation could use vmcb02 instead of vmcb01 when an L2 guest executes these instructions and L1 does not intercept them. The issue is resolved by stable kernel commits that consistently use vmcb01 for this emulation path.

Likely exposure

Exposure is most likely on Linux systems running KVM with AMD SVM nested virtualization and affected kernel versions. Non-virtualization hosts, non-KVM systems, or environments without nested SVM usage appear less exposed based on the provided description.

Exploitation context

The provided sources do not show CISA KEV listing or active exploitation. CVSS indicates local access with low privileges and no user interaction, but the triggering condition is specific to nested KVM SVM behavior.

Researcher notes

Key condition is L2 execution of VMLOAD/VMSAVE without L1 interception, causing KVM to reference vmcb02 incorrectly. Evidence is strongest for Linux KVM nSVM code behavior and stable fixes; exploit maturity is not established in the provided sources.

Mitigation direction

  • Apply vendor kernel updates that include the referenced stable KVM fixes.
  • Prioritize KVM hosts that permit nested AMD SVM virtualization.
  • Review Red Hat CVE, Bugzilla, and CSAF VEX entries for distribution-specific status.
  • If patching is delayed, assess whether nested virtualization can be disabled or restricted.

Validation and detection

  • Inventory Linux kernels on KVM virtualization hosts.
  • Identify hosts using AMD SVM and nested virtualization.
  • Compare installed kernel builds against vendor advisories and stable fix commits.
  • Check vulnerability scanners for CVE-2026-43133 coverage and vendor package mappings.
  • Confirm post-update kernels include the VMLOAD/VMSAVE nSVM correction.
Prepared
Confidence
medium
Sources
12

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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cwe · low confidence lookup

CWE-628: Exact CWE lookup

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cve · low confidence lookup

CVE-2026-43133 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.9 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

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.

2CVSS vectors
5Timeline events
1ADP providers
11Source links

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.9CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H25.3Linux
7.9CVSS 3.1HighCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H25.3redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.9High
CVSS 3.1 vector shape for CVE-2026-43133Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

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. ADP timelineredhat-SADP

    Reported to Red Hat.

  3. ADP timelineredhat-SADP

    Made public.

  4. CVE publishedCVE Program

    The CVE record was published.

  5. CVE updatedCVE Program

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

ADP provider summaries

redhat-SADPkernel: KVM: nSVM: Always use vmcb01 in VMLOAD/VMSAVE emulation
other:Red Hat severity ratingcvssV3_1
  • 2026-05-06T00:00:00.000Z: Reported to Red Hat.
  • 2026-05-06T00:00:00.000Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxcc3ed80ae69f454c3d904af9f65394a540099723, cc3ed80ae69f454c3d904af9f65394a540099723, cc3ed80ae69f454c3d904af9f65394a540099723, cc3ed80ae69f454c3d904af9f65394a540099723, cc3ed80ae69f454c3d904af9f65394a540099723, cc3ed80ae69f454c3d904af9f65394a540099723, cc3ed80ae69f454c3d904af9f65394a540099723unaffected
LinuxLinux5.13, 0, 5.15.202, 6.1.165, 6.6.128, 6.12.75, 6.18.16, 6.19.6, 7.0affected
Weakness

CWE details

CWE-628

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

CWE-628 · source CWE mapping

Function Call with Incorrectly Specified Arguments

Function Call with Incorrectly Specified Arguments represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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