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CVE-2025-21896

Estado: ModificadaAlta (7.8)—

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

fuse: revert back to __readahead_folio() for readahead

In commit 3eab9d7bc2f4 ("fuse: convert readahead to use folios"), the logic was converted to using the new folio readahead code, which drops the reference on the folio once it is locked, using an inferred reference on the folio. Previously we held a reference on the folio for the entire duration of the readpages call.

This is fine, however for the case for splice pipe responses where we will remove the old folio and splice in the new folio (see fuse_try_move_page()), we assume that there is a reference held on the folio for ap->folios, which is no longer the case.

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To fix this, revert back to __readahead_folio() which allows us to hold the reference on the folio for the duration of readpages until either we drop the reference ourselves in fuse_readpages_end() or the reference is dropped after it's replaced in the page cache in the splice case. This will fix the UAF bug that was reported.

CVSS

Probabilidad de explotación (EPSS)

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.

Vulnerabilidad local (AV:L) de escalada de privilegios por Use-After-Free (CWE-416) en kernel Linux; explotable sin interacción (UI:N) con permisos limitados (PR:L) para ejecución arbitraria de código.

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 PreventionThreat Intelligence ProgramRestrict Web-Based ContentPrivileged Account ManagementLimit Software InstallationBehavior Prevention on Endpoint

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfuse: revert back to __readahead_folio() for readahead\n\nIn commit 3eab9d7bc2f4 (\"fuse: convert readahead to use folios\"), the\nlogic was converted to using the new folio readahead code, which drops\nthe reference on the folio once it is locked, using an inferred\nreference on the folio. Previously we held a reference on the folio for\nthe entire duration of the readpages call.\n\nThis is fine, however for the case for splice pipe responses where we\nwill remove the old folio and splice in the new folio (see\nfuse_try_move_page()), we assume that there is a reference held on the\nfolio for ap->folios, which is no longer the case.\n\nTo fix this, revert back to __readahead_folio() which allows us to hold\nthe reference on the folio for the duration of readpages until either we\ndrop the reference ourselves in fuse_readpages_end() or the reference is\ndropped after it's replaced in the page cache in the splice case.\nThis will fix the UAF bug that was reported."
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      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: fuse: volver a __readahead_folio() para readahead. En el commit 3eab9d7bc2f4 (\"fuse: convertir readahead para usar folios\"), la lógica se convirtió para usar el nuevo código de readahead de folio, que elimina la referencia en el folio una vez bloqueado, usando una referencia inferida en el folio. Anteriormente, manteníamos una referencia en el folio durante toda la duración de la llamada a readpages. Esto es correcto, sin embargo, para el caso de las respuestas de la tubería de empalme donde eliminaremos el folio antiguo y empalmaremos en el nuevo folio (ver fuse_try_move_page()), asumimos que hay una referencia mantenida en el folio para ap->folios, lo cual ya no es el caso. Para solucionar esto, vuelva a __readahead_folio(), que nos permite mantener la referencia en el folio durante la lectura de páginas hasta que la eliminemos nosotros mismos en fuse_readpages_end() o hasta que se elimine tras ser reemplazada en la caché de páginas en el caso de empalme. Esto solucionará el error de UAF reportado."
    }
  ],
  "lastModified": "2026-07-30T06:21:55.870",
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