CVE-2025-39966

Estado: ModificadaAlta (7)—

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

iommufd: Fix race during abort for file descriptors

fput() doesn't actually call file_operations release() synchronously, it puts the file on a work queue and it will be released eventually.

This is normally fine, except for iommufd the file and the iommufd_object are tied to gether. The file has the object as it's private_data and holds a users refcount, while the object is expected to remain alive as long as the file is.

When the allocation of a new object aborts before installing the file it will fput() the file and then go on to immediately kfree() the obj. This causes a UAF once the workqueue completes the fput() and tries to decrement the users refcount.

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Fix this by putting the core code in charge of the file lifetime, and call __fput_sync() during abort to ensure that release() is called before kfree. __fput_sync() is a bit too tricky to open code in all the object implementations. Instead the objects tell the core code where the file pointer is and the core will take care of the life cycle.

If the object is successfully allocated then the file will hold a users refcount and the iommufd_object cannot be destroyed.

It is worth noting that close(); ioctl(IOMMU_DESTROY); doesn't have an issue because close() is already using a synchronous version of fput().

The UAF looks like this:

Detalles técnicos trazas, registros y código del informe original

    BUG: KASAN: slab-use-after-free in iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376
    Write of size 4 at addr ffff888059c97804 by task syz.0.46/6164

    CPU: 0 UID: 0 PID: 6164 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT(full)
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
    Call Trace:
     <TASK>
     __dump_stack lib/dump_stack.c:94 [inline]
     dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
     print_address_description mm/kasan/report.c:378 [inline]
     print_report+0xcd/0x630 mm/kasan/report.c:482
     kasan_report+0xe0/0x110 mm/kasan/report.c:595
     check_region_inline mm/kasan/generic.c:183 [inline]
     kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:189
     instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
     atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
     __refcount_dec include/linux/refcount.h:455 [inline]
     refcount_dec include/linux/refcount.h:476 [inline]
     iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376
     __fput+0x402/0xb70 fs/file_table.c:468
     task_work_run+0x14d/0x240 kernel/task_work.c:227
     resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
     exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43
     exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
     syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
     syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
     do_syscall_64+0x41c/0x4c0 arch/x86/entry/syscall_64.c:100
     entry_SYSCALL_64_after_hwframe+0x77/0x7f

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Puntuación base: 7

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.11%
Percentil entre todas las CVEs puntuadas: 1
Fecha de la puntuación: 6/10/2026

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).

🎯 Técnicas ATT&CK

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

ExplotaciónT1068 Exploitation for Privilege Escalationprivilege escalation75 %

CVE en kernel Linux con acceso local (AV:L), PR:L, sin interacción UI:N. CWE-362 indica race condition. La pista y el patrón de escalada de privilegios mediante explotación de kernel justifican T1068 como explotación e impacto.

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 Program Execution Prevention Application Isolation and Sandboxing Exploit Protection Update Software

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

CWE-362

Referencias

JSON original (NVD)

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  "id": "CVE-2025-39966",
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        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\niommufd: Fix race during abort for file descriptors\n\nfput() doesn't actually call file_operations release() synchronously, it\nputs the file on a work queue and it will be released eventually.\n\nThis is normally fine, except for iommufd the file and the iommufd_object\nare tied to gether. The file has the object as it's private_data and holds\na users refcount, while the object is expected to remain alive as long as\nthe file is.\n\nWhen the allocation of a new object aborts before installing the file it\nwill fput() the file and then go on to immediately kfree() the obj. This\ncauses a UAF once the workqueue completes the fput() and tries to\ndecrement the users refcount.\n\nFix this by putting the core code in charge of the file lifetime, and call\n__fput_sync() during abort to ensure that release() is called before\nkfree. __fput_sync() is a bit too tricky to open code in all the object\nimplementations. Instead the objects tell the core code where the file\npointer is and the core will take care of the life cycle.\n\nIf the object is successfully allocated then the file will hold a users\nrefcount and the iommufd_object cannot be destroyed.\n\nIt is worth noting that close(); ioctl(IOMMU_DESTROY); doesn't have an\nissue because close() is already using a synchronous version of fput().\n\nThe UAF looks like this:\n\n    BUG: KASAN: slab-use-after-free in iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376\n    Write of size 4 at addr ffff888059c97804 by task syz.0.46/6164\n\n    CPU: 0 UID: 0 PID: 6164 Comm: syz.0.46 Not tainted syzkaller #0 PREEMPT(full)\n    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025\n    Call Trace:\n     <TASK>\n     __dump_stack lib/dump_stack.c:94 [inline]\n     dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120\n     print_address_description mm/kasan/report.c:378 [inline]\n     print_report+0xcd/0x630 mm/kasan/report.c:482\n     kasan_report+0xe0/0x110 mm/kasan/report.c:595\n     check_region_inline mm/kasan/generic.c:183 [inline]\n     kasan_check_range+0x100/0x1b0 mm/kasan/generic.c:189\n     instrument_atomic_read_write include/linux/instrumented.h:96 [inline]\n     atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]\n     __refcount_dec include/linux/refcount.h:455 [inline]\n     refcount_dec include/linux/refcount.h:476 [inline]\n     iommufd_eventq_fops_release+0x45/0xc0 drivers/iommu/iommufd/eventq.c:376\n     __fput+0x402/0xb70 fs/file_table.c:468\n     task_work_run+0x14d/0x240 kernel/task_work.c:227\n     resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]\n     exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43\n     exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]\n     syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]\n     syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]\n     do_syscall_64+0x41c/0x4c0 arch/x86/entry/syscall_64.c:100\n     entry_SYSCALL_64_after_hwframe+0x77/0x7f"
    }
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  "lastModified": "2026-07-30T06:24:02.003",
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