CVE-2026-64513
In the Linux kernel, the following vulnerability has been resolved:
KVM: x86: Unconditionally recompute CR8 intercept on PPR update
The TPR_THRESHOLD field in the VMCS is used by VMX to induce VM exits when the guest's virtual TPR falls under the specified threshold, allowing KVM to inject previously masked interrupts.
KVM handles these VM exits in handle_tpr_below_threshold(). Commit eb90f3417a0c ("KVM: vmx: speed up TPR below threshold vmexits") optimized this function by calling apic_update_ppr() instead of raising KVM_REQ_EVENT. apic_update_ppr() then raises KVM_REQ_EVENT if there is a pending, deliverable interrupt.
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However, if there are no new interrupts pending, apic_update_ppr() does not issue the request. Thus, kvm_lapic_update_cr8_intercept() and vmx_update_cr8_intercept() are not called before VM entry, which results in a high, stale TPR_THRESHOLD. This is problematic due to the following sentence in 28.2.1.1 "VM-Execution Control Fields" in the SDM:
This error condition is typically not observed when KVM runs on a bare metal system because modern processors support APICv, which enables virtual-interrupt delivery, and which KVM uses when possible. This causes the processor to no longer generate TPR-below-threshold exits and to no longer check TPR_THRESHOLD on entry. However, when running on older platforms, or under nested virtualization on a hypervisor that does not support virtual-interrupt delivery and enforces this check (like Hyper-V) this can cause a VM entry failure with hardware error 0x7, as seen in [1].
Call kvm_lapic_update_cr8_intercept() if apic_update_ppr() does not find a deliverable interrupt (and thus does not raise KVM_REQ_EVENT). Remove calls to kvm_lapic_update_cr8_intercept() on paths that end up in apic_update_ppr(), as they now become redundant. This ensures that any path that updates the guest's PPR also figures out if KVM needs to wait for a TPR change (using TPR_THRESHOLD on VMX or CR8 intercepts on SVM).
Detalles técnicos trazas, registros y código del informe original
The following check is performed if the “use TPR shadow” VM-execution control is 1 and the “virtualize APIC accesses” and “virtual-interrupt delivery” VM-execution controls are both 0: the value of bits 3:0 of the TPR threshold VM-execution control field should not be greater than the value of bits 7:4 of VTPR.
CVSS
NVD no ha asignado puntuación CVSS a esta CVE (habitual desde el cambio de política de abril de 2026).
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.22%
- Percentil entre todas las CVEs puntuadas: 12
- Fecha de la puntuación: 5/10/2026
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).
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
JSON original (NVD)
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{
"id": "CVE-2026-64513",
"cveTags": [],
"metrics": {},
"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": "eb90f3417a0cc4880e979ccc84e41890d410ea5b",
"lessThan": "ff9c4c6428883182960cfe5c78928f0896d80ebc",
"versionType": "git"
},
{
"status": "affected",
"version": "eb90f3417a0cc4880e979ccc84e41890d410ea5b",
"lessThan": "8c8e8ac22ee17d52f9eb2bc814bca7fab90fb8df",
"versionType": "git"
},
{
"status": "affected",
"version": "eb90f3417a0cc4880e979ccc84e41890d410ea5b",
"lessThan": "bb365a506b1e6fb050c0fceaad354fe395385ef0",
"versionType": "git"
}
],
"programFiles": [
"arch/x86/kvm/lapic.c",
"arch/x86/kvm/x86.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "4.11"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "4.11",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "6.18.39",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.1.4",
"versionType": "semver",
"lessThanOrEqual": "7.1.*"
},
{
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"arch/x86/kvm/lapic.c",
"arch/x86/kvm/x86.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-07-25T10:17:37.510",
"references": [
{
"url": "https://git.kernel.org/stable/c/8c8e8ac22ee17d52f9eb2bc814bca7fab90fb8df",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/bb365a506b1e6fb050c0fceaad354fe395385ef0",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/ff9c4c6428883182960cfe5c78928f0896d80ebc",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Unconditionally recompute CR8 intercept on PPR update\n\nThe TPR_THRESHOLD field in the VMCS is used by VMX to induce VM exits\nwhen the guest's virtual TPR falls under the specified threshold,\nallowing KVM to inject previously masked interrupts.\n\nKVM handles these VM exits in handle_tpr_below_threshold().\nCommit eb90f3417a0c (\"KVM: vmx: speed up TPR below threshold vmexits\")\noptimized this function by calling apic_update_ppr() instead of raising\nKVM_REQ_EVENT. apic_update_ppr() then raises KVM_REQ_EVENT if there is\na pending, deliverable interrupt.\n\nHowever, if there are no new interrupts pending, apic_update_ppr() does\nnot issue the request. Thus, kvm_lapic_update_cr8_intercept() and\nvmx_update_cr8_intercept() are not called before VM entry, which results\nin a high, stale TPR_THRESHOLD. This is problematic due to the following\nsentence in 28.2.1.1 \"VM-Execution Control Fields\" in the SDM:\n\n The following check is performed if the “use TPR shadow” VM-execution\n control is 1 and the “virtualize APIC accesses” and “virtual-interrupt\n delivery” VM-execution controls are both 0: the value of bits 3:0 of\n the TPR threshold VM-execution control field should not be greater\n than the value of bits 7:4 of VTPR.\n\nThis error condition is typically not observed when KVM runs on a bare\nmetal system because modern processors support APICv, which enables\nvirtual-interrupt delivery, and which KVM uses when possible. This\ncauses the processor to no longer generate TPR-below-threshold exits\nand to no longer check TPR_THRESHOLD on entry. However, when running\non older platforms, or under nested virtualization on a hypervisor that\ndoes not support virtual-interrupt delivery and enforces this check\n(like Hyper-V) this can cause a VM entry failure with hardware error\n0x7, as seen in [1].\n\nCall kvm_lapic_update_cr8_intercept() if apic_update_ppr() does not\nfind a deliverable interrupt (and thus does not raise KVM_REQ_EVENT).\nRemove calls to kvm_lapic_update_cr8_intercept() on paths that end up in\napic_update_ppr(), as they now become redundant. This ensures that any\npath that updates the guest's PPR also figures out if KVM needs to wait\nfor a TPR change (using TPR_THRESHOLD on VMX or CR8 intercepts on SVM)."
}
],
"lastModified": "2026-08-17T05:17:57.520",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}