CVE-2026-22980

Estado: ModificadaAlta (7.8)—

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

nfsd: provide locking for v4_end_grace

Writing to v4_end_grace can race with server shutdown and result in memory being accessed after it was freed - reclaim_str_hashtbl in particularly.

We cannot hold nfsd_mutex across the nfsd4_end_grace() call as that is held while client_tracking_op->init() is called and that can wait for an upcall to nfsdcltrack which can write to v4_end_grace, resulting in a deadlock.

nfsd4_end_grace() is also called by the landromat work queue and this doesn't require locking as server shutdown will stop the work and wait for it before freeing anything that nfsd4_end_grace() might access.

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However, we must be sure that writing to v4_end_grace doesn't restart the work item after shutdown has already waited for it. For this we add a new flag protected with nn->client_lock. It is set only while it is safe to make client tracking calls, and v4_end_grace only schedules work while the flag is set with the spinlock held.

So this patch adds a nfsd_net field "client_tracking_active" which is set as described. Another field "grace_end_forced", is set when v4_end_grace is written. After this is set, and providing client_tracking_active is set, the laundromat is scheduled. This "grace_end_forced" field bypasses other checks for whether the grace period has finished.

This resolves a race which can result in 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: 0.15%
Percentil entre todas las CVEs puntuadas: 4
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).

🎯 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 Interpreterexecution60 %

Vulnerabilidad de use-after-free (CWE-416) en acceso local (AV:L, PR:L) del kernel Linux que permite ejecutar código con altos privilegios (C:H, I:H, A:H) tras escalada de privilegios.

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\nnfsd: provide locking for v4_end_grace\n\nWriting to v4_end_grace can race with server shutdown and result in\nmemory being accessed after it was freed - reclaim_str_hashtbl in\nparticularly.\n\nWe cannot hold nfsd_mutex across the nfsd4_end_grace() call as that is\nheld while client_tracking_op->init() is called and that can wait for\nan upcall to nfsdcltrack which can write to v4_end_grace, resulting in a\ndeadlock.\n\nnfsd4_end_grace() is also called by the landromat work queue and this\ndoesn't require locking as server shutdown will stop the work and wait\nfor it before freeing anything that nfsd4_end_grace() might access.\n\nHowever, we must be sure that writing to v4_end_grace doesn't restart\nthe work item after shutdown has already waited for it.  For this we\nadd a new flag protected with nn->client_lock.  It is set only while it\nis safe to make client tracking calls, and v4_end_grace only schedules\nwork while the flag is set with the spinlock held.\n\nSo this patch adds a nfsd_net field \"client_tracking_active\" which is\nset as described.  Another field \"grace_end_forced\", is set when\nv4_end_grace is written.  After this is set, and providing\nclient_tracking_active is set, the laundromat is scheduled.\nThis \"grace_end_forced\" field bypasses other checks for whether the\ngrace period has finished.\n\nThis resolves a race which can result in use-after-free."
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      "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nnfsd: proporcionar bloqueo para v4_end_grace\n\nEscribir en v4_end_grace puede competir con el apagado del servidor y resultar en que la memoria sea accedida después de haber sido liberada - reclaim_str_hashtbl en particular.\n\nNo podemos mantener nfsd_mutex durante la llamada a nfsd4_end_grace() ya que se mantiene mientras se llama a client_tracking_op-&gt;init() y eso puede esperar una llamada ascendente a nfsdcltrack que puede escribir en v4_end_grace, resultando en un interbloqueo.\n\nnfsd4_end_grace() también es llamada por la cola de trabajo 'landromat' y esto no requiere bloqueo ya que el apagado del servidor detendrá el trabajo y esperará por él antes de liberar cualquier cosa a la que nfsd4_end_grace() pudiera acceder.\n\nSin embargo, debemos asegurarnos de que escribir en v4_end_grace no reinicie el elemento de trabajo después de que el apagado ya lo haya esperado. Para esto añadimos una nueva bandera protegida con nn-&gt;client_lock. Se establece solo mientras es seguro realizar llamadas de seguimiento de cliente, y v4_end_grace solo programa trabajo mientras la bandera está establecida con el spinlock mantenido.\n\nAsí, este parche añade un campo nfsd_net 'client_tracking_active' que se establece como se describe. Otro campo 'grace_end_forced', se establece cuando se escribe en v4_end_grace. Después de que esto se establece, y siempre que client_tracking_active esté establecido, el 'laundromat' es programado. Este campo 'grace_end_forced' omite otras comprobaciones para determinar si el período de gracia ha terminado.\n\nEsto resuelve una condición de carrera que puede resultar en uso después de liberación."
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