CVE-2026-31444

Estado: AnalizadaCrítica (9.8)—

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

ksmbd: fix use-after-free and NULL deref in smb_grant_oplock()

smb_grant_oplock() has two issues in the oplock publication sequence:

Fix by restructuring the publication sequence to eliminate post-publish failure:

This also requires splitting add_lease_global_list() to take a preallocated lease_table and changing its return type from int to void, since it can no longer fail.

Detalles técnicos trazas, registros y código del informe original

1) opinfo is linked into ci->m_op_list (via opinfo_add) before
   add_lease_global_list() is called.  If add_lease_global_list()
   fails (kmalloc returns NULL), the error path frees the opinfo
   via __free_opinfo() while it is still linked in ci->m_op_list.
   Concurrent m_op_list readers (opinfo_get_list, or direct iteration
   in smb_break_all_levII_oplock) dereference the freed node.

2) opinfo->o_fp is assigned after add_lease_global_list() publishes
   the opinfo on the global lease list.  A concurrent
   find_same_lease_key() can walk the lease list and dereference
   opinfo->o_fp->f_ci while o_fp is still NULL.

- Set opinfo->o_fp before any list publication (fixes NULL deref).
- Preallocate lease_table via alloc_lease_table() before opinfo_add()
  so add_lease_global_list() becomes infallible after publication.
- Keep the original m_op_list publication order (opinfo_add before
  lease list) so concurrent opens via same_client_has_lease() and
  opinfo_get_list() still see the in-flight grant.
- Use opinfo_put() instead of __free_opinfo() on err_out so that
  the RCU-deferred free path is used.

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Puntuación base: 9.8

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.65%
Percentil entre todas las CVEs puntuadas: 50
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.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access75 %
Impacto principalT1059 Command and Scripting Interpreterexecution65 %
Impacto secundarioT1499.004 Application or System Exploitationimpact60 %

Kernel SMB vuln in ksmbd (AV:N/AC:L/PR:N) permite RCE vía T1190. Use-after-free/NULL deref resulta en ejecución de código (T1059) o DoS (T1499.004).

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

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Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

CWE-416

Referencias

JSON original (NVD)

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free and NULL deref in smb_grant_oplock()\n\nsmb_grant_oplock() has two issues in the oplock publication sequence:\n\n1) opinfo is linked into ci->m_op_list (via opinfo_add) before\n   add_lease_global_list() is called.  If add_lease_global_list()\n   fails (kmalloc returns NULL), the error path frees the opinfo\n   via __free_opinfo() while it is still linked in ci->m_op_list.\n   Concurrent m_op_list readers (opinfo_get_list, or direct iteration\n   in smb_break_all_levII_oplock) dereference the freed node.\n\n2) opinfo->o_fp is assigned after add_lease_global_list() publishes\n   the opinfo on the global lease list.  A concurrent\n   find_same_lease_key() can walk the lease list and dereference\n   opinfo->o_fp->f_ci while o_fp is still NULL.\n\nFix by restructuring the publication sequence to eliminate post-publish\nfailure:\n\n- Set opinfo->o_fp before any list publication (fixes NULL deref).\n- Preallocate lease_table via alloc_lease_table() before opinfo_add()\n  so add_lease_global_list() becomes infallible after publication.\n- Keep the original m_op_list publication order (opinfo_add before\n  lease list) so concurrent opens via same_client_has_lease() and\n  opinfo_get_list() still see the in-flight grant.\n- Use opinfo_put() instead of __free_opinfo() on err_out so that\n  the RCU-deferred free path is used.\n\nThis also requires splitting add_lease_global_list() to take a\npreallocated lease_table and changing its return type from int to void,\nsince it can no longer fail."
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