CVE-2025-40300
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: x86/vmscape: Add conditional IBPB mitigation VMSCAPE is a vulnerability that exploits insufficient branch predictor isolation between a guest and a userspace hypervisor (like QEMU). Existing mitigations already protect kernel/KVM from a malicious guest. Userspace can additionally be protected by flushing the branch predictors after a VMexit. Since it is the userspace that consumes the poisoned branch predictors, conditionally issue an IBPB after a VMexit and before returning to userspace. Workloads that frequently switch between hypervisor and userspace will incur the most overhead from the new IBPB. This new IBPB is not integrated with the existing IBPB sites. For instance, a task can use the existing speculation control prctl() to get an IBPB at context switch time. With this implementation, the IBPB is doubled up: one at context switch and another before running userspace. The intent is to integrate and optimize these cases post-embargo. [ dhansen: elaborate on suboptimal IBPB solution ]
Severity
MEDIUM
CVSS score
5.5
(v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2025-09-11 17:15:45.680000
Last modified
2026-10-19 21:10:00.160000
View original CVE JSON
{
"id": "CVE-2025-40300",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2025-09-11T17:15:45.680",
"lastModified": "2026-10-19T21:10:00.160",
"vulnStatus": "Modified",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/vmscape: Add conditional IBPB mitigation\n\nVMSCAPE is a vulnerability that exploits insufficient branch predictor\nisolation between a guest and a userspace hypervisor (like QEMU). Existing\nmitigations already protect kernel/KVM from a malicious guest. Userspace\ncan additionally be protected by flushing the branch predictors after a\nVMexit.\n\nSince it is the userspace that consumes the poisoned branch predictors,\nconditionally issue an IBPB after a VMexit and before returning to\nuserspace. Workloads that frequently switch between hypervisor and\nuserspace will incur the most overhead from the new IBPB.\n\nThis new IBPB is not integrated with the existing IBPB sites. For\ninstance, a task can use the existing speculation control prctl() to\nget an IBPB at context switch time. With this implementation, the\nIBPB is doubled up: one at context switch and another before running\nuserspace.\n\nThe intent is to integrate and optimize these cases post-embargo.\n\n[ dhansen: elaborate on suboptimal IBPB solution ]"
},
{
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"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nx86/vmscape: Añadir mitigación condicional de IBPB\n\nVMSCAPE es una vulnerabilidad que explota el aislamiento insuficiente del predictor de ramas entre un invitado y un hipervisor en espacio de usuario (como QEMU). Las mitigaciones existentes ya protegen al kernel/KVM de un invitado malicioso. El espacio de usuario puede protegerse adicionalmente vaciando los predictores de ramas después de un VMexit.\n\nDado que es el espacio de usuario el que consume los predictores de ramas envenenados, se emite condicionalmente un IBPB después de un VMexit y antes de regresar al espacio de usuario. Las cargas de trabajo que con frecuencia cambian entre el hipervisor y el espacio de usuario incurrirán en la mayor sobrecarga del nuevo IBPB.\n\nEste nuevo IBPB no está integrado con los sitios IBPB existentes. Por ejemplo, una tarea puede usar el prctl() de control de especulación existente para obtener un IBPB en el momento del cambio de contexto. Con esta implementación, el IBPB se duplica: uno en el cambio de contexto y otro antes de ejecutar el espacio de usuario.\n\nLa intención es integrar y optimizar estos casos post-embargo.\n\n[ dhansen: elaborar sobre la solución IBPB subóptima ]"
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{
"url": "https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html",
"source": "af854a3a-2127-422b-91ae-364da2661108",
"tags": [
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]
},
{
"url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
},
{
"url": "https://cert-portal.siemens.com/productcert/html/ssa-032379.html",
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
},
{
"url": "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
}
]
}