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CVE-2026-63941

Estado: Pendiente de análisisAlta (8.8)—

In the Linux kernel, the following vulnerability has been resolved:

KVM: arm64: Correctly cap ZCR_EL2 provided by a guest hypervisor

ZCR_EL2 can be updated by a VHE guest hypervisor either using ZCR_EL2 (which traps) or ZCR_EL1 (which does not trap). KVM handles both in different way:

- on ZCR_EL1 access, we do absolutely nothing.

On restoring the SVE context for an L2 guest, we directly restore the guest hypervisor's view of ZCR_EL2 into the physical ZCR_EL2. If the guest's view of the register was updated using the ZCR_EL2 accessor, the value has already been sanitised (with the caveat mentioned above).

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But if the guest used ZCR_EL1, the raw value is written into the HW, and the L2 guest can now access VLs that it shouldn't.

Fix all the above by moving the VL capping to the restore points, ensuring that:

Additionally, move ZCR_EL2 to be a sanitised register, ensuring that only the LEN field is actually stateful. This requires some creative construction of the RES0 mask, as the sysreg generation script does not yet generate RAZ/WI fields.

[maz: rewrote commit message, tidy up access_zcr_el2()]

Detalles técnicos trazas, registros y código del informe original
- on ZCR_EL2 trap, ZCR_EL2.LEN is immediately capped at the VM's own
  VL limit. This has the potential to break existing SW that relies
  on the full LEN field to be stateful.

- the HW is always programmed with a capped value, irrespective of
  the accessor being used,

- the ZCR_EL2.LEN field is always completely stateful, irrespective
  of the accessor being used.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

Vulnerabilidad local en kernel Linux (AV:L, PR:L) que permite a un hipervisor invitado eludir restricciones de virtualización y acceder a niveles de privilegio no autorizados mediante manipulación de registros ZCR_EL2, escalando privilegios en el contexto del host.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Threat Intelligence ProgramExecution PreventionApplication Isolation and SandboxingExploit ProtectionUpdate Software

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux KernelAI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-63941",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "CHANGED",
          "version": "3.1",
          "baseScore": 8.8,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 6,
        "exploitabilityScore": 2
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "b3d29a8230998b36afecf494b199211d26052785",
              "lessThan": "742a9b5ccd8c46caf983ca90c94f855466968e34",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "b3d29a8230998b36afecf494b199211d26052785",
              "lessThan": "83726330748981372bde86ed5411d7b306612991",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "arch/arm64/include/asm/kvm_host.h",
            "arch/arm64/kvm/hyp/include/hyp/switch.h",
            "arch/arm64/kvm/nested.c",
            "arch/arm64/kvm/sys_regs.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.11"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.11",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver",
              "lessThanOrEqual": "7.0.*"
            },
            {
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "arch/arm64/include/asm/kvm_host.h",
            "arch/arm64/kvm/hyp/include/hyp/switch.h",
            "arch/arm64/kvm/nested.c",
            "arch/arm64/kvm/sys_regs.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-07-19T16:17:12.643",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/742a9b5ccd8c46caf983ca90c94f855466968e34",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/83726330748981372bde86ed5411d7b306612991",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: arm64: Correctly cap ZCR_EL2 provided by a guest hypervisor\n\nZCR_EL2 can be updated by a VHE guest hypervisor either using ZCR_EL2\n(which traps) or ZCR_EL1 (which does not trap). KVM handles both in\ndifferent way:\n\n- on ZCR_EL2 trap, ZCR_EL2.LEN is immediately capped at the VM's own\n  VL limit. This has the potential to break existing SW that relies\n  on the full LEN field to be stateful.\n\n- on ZCR_EL1 access, we do absolutely nothing.\n\nOn restoring the SVE context for an L2 guest, we directly restore the\nguest hypervisor's view of ZCR_EL2 into the physical ZCR_EL2. If the\nguest's view of the register was updated using the ZCR_EL2 accessor,\nthe value has already been sanitised (with the caveat mentioned above).\n\nBut if the guest used ZCR_EL1, the raw value is written into the HW,\nand the L2 guest can now access VLs that it shouldn't.\n\nFix all the above by moving the VL capping to the restore points,\nensuring that:\n\n- the HW is always programmed with a capped value, irrespective of\n  the accessor being used,\n\n- the ZCR_EL2.LEN field is always completely stateful, irrespective\n  of the accessor being used.\n\nAdditionally, move ZCR_EL2 to be a sanitised register, ensuring that\nonly the LEN field is actually stateful. This requires some creative\nconstruction of the RES0 mask, as the sysreg generation script does\nnot yet generate RAZ/WI fields.\n\n[maz: rewrote commit message, tidy up access_zcr_el2()]"
    }
  ],
  "lastModified": "2026-07-27T17:44:23.777",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}