CVE-2025-40026
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O When completing emulation of instruction that generated a userspace exit for I/O, don't recheck L1 intercepts as KVM has already finished that phase of instruction execution, i.e. has already committed to allowing L2 to perform I/O. If L1 (or host userspace) modifies the I/O permission bitmaps during the exit to userspace, KVM will treat the access as being intercepted despite already having emulated the I/O access. Pivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation. Of the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the intended "recipient") can reach the code in question. gp_interception()'s use is mutually exclusive with is_guest_mode(), and complete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with EMULTYPE_SKIP. The bad behavior was detected by a syzkaller program that toggles port I/O interception during the userspace I/O exit, ultimately resulting in a WARN on vcpu->arch.pio.count being non-zero due to KVM no completing emulation of the I/O instruction. WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm] Modules linked in: kvm_intel kvm irqbypass CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm] PKRU: 55555554 Call Trace: <TASK> kvm_fast_pio+0xd6/0x1d0 [kvm] vmx_handle_exit+0x149/0x610 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm] kvm_vcpu_ioctl+0x244/0x8c0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0x5d/0xc60 entry_SYSCALL_64_after_hwframe+0x4b/0x53 </TASK>
Severity
HIGH
CVSS score
7.9
(v3.1)
Vulnerability status
Deferred
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-10-28 10:15:42.167000
Last modified
2026-10-19 21:10:00.160000
View original CVE JSON
{
"id": "CVE-2025-40026",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2025-10-28T10:15:42.167",
"lastModified": "2026-10-19T21:10:00.160",
"vulnStatus": "Deferred",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Don't (re)check L1 intercepts when completing userspace I/O\n\nWhen completing emulation of instruction that generated a userspace exit\nfor I/O, don't recheck L1 intercepts as KVM has already finished that\nphase of instruction execution, i.e. has already committed to allowing L2\nto perform I/O. If L1 (or host userspace) modifies the I/O permission\nbitmaps during the exit to userspace, KVM will treat the access as being\nintercepted despite already having emulated the I/O access.\n\nPivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation.\nOf the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the\nintended \"recipient\") can reach the code in question. gp_interception()'s\nuse is mutually exclusive with is_guest_mode(), and\ncomplete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with\nEMULTYPE_SKIP.\n\nThe bad behavior was detected by a syzkaller program that toggles port I/O\ninterception during the userspace I/O exit, ultimately resulting in a WARN\non vcpu->arch.pio.count being non-zero due to KVM no completing emulation\nof the I/O instruction.\n\n WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm]\n Modules linked in: kvm_intel kvm irqbypass\n CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm]\n PKRU: 55555554\n Call Trace:\n <TASK>\n kvm_fast_pio+0xd6/0x1d0 [kvm]\n vmx_handle_exit+0x149/0x610 [kvm_intel]\n kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm]\n kvm_vcpu_ioctl+0x244/0x8c0 [kvm]\n __x64_sys_ioctl+0x8a/0xd0\n do_syscall_64+0x5d/0xc60\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n </TASK>"
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nKVM: x86: No (re)verificar las intercepciones L1 al completar la E/S del espacio de usuario\n\nAl completar la emulación de una instrucción que generó una salida al espacio de usuario para E/S, no volver a verificar las intercepciones L1 ya que KVM ya ha terminado esa fase de ejecución de la instrucción, es decir, ya se ha comprometido a permitir que L2 realice E/S. Si L1 (o el espacio de usuario del host) modifica los mapas de bits de permisos de E/S durante la salida al espacio de usuario, KVM tratará el acceso como interceptado a pesar de haber emulado ya el acceso de E/S.\n\nBasarse en EMULTYPE_NO_DECODE para detectar que KVM está completando la emulación. De los tres usuarios de EMULTYPE_NO_DECODE, solo complete_emulated_io() (el 'destinatario' previsto) puede alcanzar el código en cuestión. El uso de gp_interception() es mutuamente excluyente con is_guest_mode(), y complete_emulated_insn_gp() empareja incondicionalmente EMULTYPE_NO_DECODE con EMULTYPE_SKIP.\n\nEl comportamiento erróneo fue detectado por un programa syzkaller que alterna la intercepción de E/S del puerto durante la salida de E/S del espacio de usuario, lo que finalmente resultó en una ADVERTENCIA (WARN) sobre vcpu->arch.pio.count siendo distinto de cero debido a que KVM no completó la emulación de la instrucción de E/S.\n\n ADVERTENCIA: CPU: 23 PID: 1083 en arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm]\n Módulos enlazados: kvm_intel kvm irqbypass\n CPU: 23 UID: 1000 PID: 1083 Comm: repro No contaminado 6.16.0-rc5-c1610d2d66b1-next-vm #74 NINGUNO\n Nombre del hardware: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015\n RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm]\n PKRU: 55555554\n Traza de llamada:\n <TAREA>\n kvm_fast_pio+0xd6/0x1d0 [kvm]\n vmx_handle_exit+0x149/0x610 [kvm_intel]\n kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm]\n kvm_vcpu_ioctl+0x244/0x8c0 [kvm]\n __x64_sys_ioctl+0x8a/0xd0\n do_syscall_64+0x5d/0xc60\n entry_SYSCALL_64_after_hwframe+0x4b/0x53\n </TAREA>"
}
],
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "unaffected",
"programFiles": [
"arch/x86/kvm/emulate.c",
"arch/x86/kvm/kvm_emulate.h",
"arch/x86/kvm/x86.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "8a76d7f25f8f24fc5a328c8e15e4a7313cf141b9",
"lessThan": "a908eca437789589dd4624da428614c1275064dc",
"versionType": "git",
"status": "affected"
},
{
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"lessThan": "00338255bb1f422642fb2798ebe92e93b6e4209b",
"versionType": "git",
"status": "affected"
},
{
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"lessThan": "e0ce3ed1048a47986d15aef1a98ebda25560d257",
"versionType": "git",
"status": "affected"
},
{
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"versionType": "git",
"status": "affected"
},
{
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"versionType": "git",
"status": "affected"
},
{
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"versionType": "git",
"status": "affected"
},
{
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"versionType": "git",
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"versionType": "git",
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},
{
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"versionType": "git",
"status": "affected"
}
]
},
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "affected",
"programFiles": [
"arch/x86/kvm/emulate.c",
"arch/x86/kvm/kvm_emulate.h",
"arch/x86/kvm/x86.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "3.0",
"status": "affected"
},
{
"version": "0",
"lessThan": "3.0",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "5.4.301",
"lessThanOrEqual": "5.4.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "5.10.246",
"lessThanOrEqual": "5.10.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "5.15.195",
"lessThanOrEqual": "5.15.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.1.157",
"lessThanOrEqual": "6.1.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.6.111",
"lessThanOrEqual": "6.6.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.12.52",
"lessThanOrEqual": "6.12.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.16.12",
"lessThanOrEqual": "6.16.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.17.2",
"lessThanOrEqual": "6.17.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.18",
"lessThanOrEqual": "*",
"versionType": "original_commit_for_fix",
"status": "unaffected"
}
]
}
]
}
],
"metrics": {
"cvssMetricV31": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary",
"cvssData": {
"version": "3.1",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:H",
"baseScore": 7.9,
"baseSeverity": "HIGH",
"attackVector": "LOCAL",
"attackComplexity": "LOW",
"privilegesRequired": "LOW",
"userInteraction": "NONE",
"scope": "CHANGED",
"confidentialityImpact": "LOW",
"integrityImpact": "LOW",
"availabilityImpact": "HIGH"
},
"exploitabilityScore": 2.0,
"impactScore": 5.3
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"timestamp": "2026-10-15T21:56:14.274469Z",
"id": "CVE-2025-40026",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "partial"
}
],
"role": "CISA Coordinator",
"version": "2.0.3"
}
}
]
},
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