CVE-2022-49834

Estado: ModificadaAlta (7.8)—

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

nilfs2: fix use-after-free bug of ns_writer on remount

If a nilfs2 filesystem is downgraded to read-only due to metadata corruption on disk and is remounted read/write, or if emergency read-only remount is performed, detaching a log writer and synchronizing the filesystem can be done at the same time.

In these cases, use-after-free of the log writer (hereinafter nilfs->ns_writer) can happen as shown in the scenario below:

While Task1 is sleeping, nilfs->ns_writer is freed by Task2. After Task1 waked up, Task1 accesses nilfs->ns_writer which is already freed. This scenario diagram is based on the Shigeru Yoshida's post [1].

Leer descripción completaMostrar menos

This patch fixes the issue by not detaching nilfs->ns_writer on remount so that this UAF race doesn't happen. Along with this change, this patch also inserts a few necessary read-only checks with superblock instance where only the ns_writer pointer was used to check if the filesystem is read-only.

Detalles técnicos trazas, registros y código del informe original

 Task1                               Task2
 --------------------------------    ------------------------------
 nilfs_construct_segment
   nilfs_segctor_sync
     init_wait
     init_waitqueue_entry
     add_wait_queue
     schedule
                                     nilfs_remount (R/W remount case)
				       nilfs_attach_log_writer
                                         nilfs_detach_log_writer
                                           nilfs_segctor_destroy
                                             kfree
     finish_wait
       _raw_spin_lock_irqsave
         __raw_spin_lock_irqsave
           do_raw_spin_lock
             debug_spin_lock_before  <-- use-after-free

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Puntuación base: 7.8

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: 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 escalation85 %
Impacto principalT1059 Command and Scripting Interpreterexecution75 %

Vulnerabilidad UAF (CWE-416) en kernel Linux con acceso local (AV:L) sin interacción del usuario (UI:N) que permite escalada de privilegios mediante corrupción de memoria; el impacto es ejecución de código arbitrario.

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

Execution Prevention Threat Intelligence Program Restrict Web-Based Content Privileged Account Management Limit Software Installation Behavior Prevention on Endpoint

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

CWE-416

Referencias

JSON original (NVD)

Mostrar

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnilfs2: fix use-after-free bug of ns_writer on remount\n\nIf a nilfs2 filesystem is downgraded to read-only due to metadata\ncorruption on disk and is remounted read/write, or if emergency read-only\nremount is performed, detaching a log writer and synchronizing the\nfilesystem can be done at the same time.\n\nIn these cases, use-after-free of the log writer (hereinafter\nnilfs->ns_writer) can happen as shown in the scenario below:\n\n Task1                               Task2\n --------------------------------    ------------------------------\n nilfs_construct_segment\n   nilfs_segctor_sync\n     init_wait\n     init_waitqueue_entry\n     add_wait_queue\n     schedule\n                                     nilfs_remount (R/W remount case)\n\t\t\t\t       nilfs_attach_log_writer\n                                         nilfs_detach_log_writer\n                                           nilfs_segctor_destroy\n                                             kfree\n     finish_wait\n       _raw_spin_lock_irqsave\n         __raw_spin_lock_irqsave\n           do_raw_spin_lock\n             debug_spin_lock_before  <-- use-after-free\n\nWhile Task1 is sleeping, nilfs->ns_writer is freed by Task2.  After Task1\nwaked up, Task1 accesses nilfs->ns_writer which is already freed.  This\nscenario diagram is based on the Shigeru Yoshida's post [1].\n\nThis patch fixes the issue by not detaching nilfs->ns_writer on remount so\nthat this UAF race doesn't happen.  Along with this change, this patch\nalso inserts a few necessary read-only checks with superblock instance\nwhere only the ns_writer pointer was used to check if the filesystem is\nread-only."
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      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: nilfs2: corrige el error de use-after-free de ns_writer al volver a montar Si un sistema de archivos nilfs2 se degrada a solo lectura debido a la corrupción de metadatos en el disco y se vuelve a montar en modo de lectura/escritura, o si se realiza un remontaje de solo lectura de emergencia, se puede desconectar un escritor de registros y sincronizar el sistema de archivos al mismo tiempo. En estos casos, el use-after-free del escritor de registros (en adelante nilfs-&gt;ns_writer) puede ocurrir como se muestra en el siguiente escenario: Tarea1 Tarea2 -------------------------------- ---------------------------------- nilfs_construct_segment nilfs_segctor_sync init_wait init_waitqueue_entry add_wait_queue schedule nilfs_remount (caso de remontaje de R/W) nilfs_attach_log_writer nilfs_detach_log_writer nilfs_segctor_destroy kfree finish_wait _raw_spin_lock_irqsave __raw_spin_lock_irqsave do_raw_spin_lock debug_spin_lock_before &lt;-- use-after-free Mientras la Tarea1 está en reposo, nilfs-&gt;ns_writer es liberado por la Tarea2. Después de que la Tarea1 se despierta, la Tarea1 accede a nilfs-&gt;ns_writer que ya está liberado. Este diagrama de escenario se basa en la publicación de Shigeru Yoshida [1]. Este parche corrige el problema al no desvincular nilfs-&gt;ns_writer al volver a montar, lo que evita que se produzca esta ejecución UAF. Además de este cambio, este parche también inserta algunas comprobaciones de solo lectura necesarias con la instancia de superbloque, donde solo se usaba el puntero ns_writer para comprobar si el sistema de archivos era de solo lectura."
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