CVE-2026-31703
Estado: ModificadaAlta (7.8)—
In the Linux kernel, the following vulnerability has been resolved:
writeback: Fix use after free in inode_switch_wbs_work_fn()
inode_switch_wbs_work_fn() has a loop like:
Now adding of items to the list looks like:
Because inode_switch_wbs_work_fn() loops when processing isw items, it can happen that wb->switch_work is pending while wb->switch_wbs_ctxs is empty. This is a problem because in that case wb can get freed (no isw items -> no wb reference) while the work is still pending causing use-after-free issues.
We cannot just fix this by cancelling work when freeing wb because that could still trigger problematic 0 -> 1 transitions on wb refcount due to wb_get() in inode_switch_wbs_work_fn().
Leer descripción completaMostrar menos
It could be all handled with more careful code but that seems unnecessarily complex so let's avoid that until it is proven that the looping actually brings practical benefit. Just remove the loop from inode_switch_wbs_work_fn() instead. That way when wb_queue_isw() queues work, we are guaranteed we have added the first item to wb->switch_wbs_ctxs and nobody is going to remove it (and drop the wb reference it holds) until the queued work runs.
Detalles técnicos trazas, registros y código del informe original
wb_get(new_wb);
while (1) {
list = llist_del_all(&new_wb->switch_wbs_ctxs);
/* Nothing to do? */
if (!list)
break;
... process the items ...
}
wb_queue_isw()
if (llist_add(&isw->list, &wb->switch_wbs_ctxs))
queue_work(isw_wq, &wb->switch_work);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: 0.17%
- Percentil entre todas las CVEs puntuadas: 6
- 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.
- Explotación
T1068Exploitation for Privilege Escalationprivilege escalation85 % - Impacto principal
T1059Command and Scripting Interpreterexecution70 %
Vulnerabilidad use-after-free (CWE-416) en kernel Linux con AV:L/PR:L/UI:N permite escalada de privilegios local. La corrupción de memoria podría lograr ejecución 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
Tecnologías afectadas (1)
CWE
- CWE-416
- CWE-825
Referencias
- https://git.kernel.org/stable/c/028103656b84273c73e9e271cf95c9f3421f4b8a
- https://git.kernel.org/stable/c/156cc63691c1f20905510b1007896e090355e6c2
- https://git.kernel.org/stable/c/19ec404b079be057b387643ba0c69bbcc5867c35
- https://git.kernel.org/stable/c/382cf81cae89e58d22b4bdc38891cd4d0b9ba921
- https://git.kernel.org/stable/c/6689f01d6740cf358932b3e97ee968c6099800d9
- https://git.kernel.org/stable/c/9223e5f30403a9b506d6d0bff4f2e29a2d7d46af
- https://access.redhat.com/security/cve/CVE-2026-31703
- https://bugzilla.redhat.com/show_bug.cgi?id=2464385
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31703.json
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nwriteback: Fix use after free in inode_switch_wbs_work_fn()\n\ninode_switch_wbs_work_fn() has a loop like:\n\n wb_get(new_wb);\n while (1) {\n list = llist_del_all(&new_wb->switch_wbs_ctxs);\n /* Nothing to do? */\n if (!list)\n break;\n ... process the items ...\n }\n\nNow adding of items to the list looks like:\n\nwb_queue_isw()\n if (llist_add(&isw->list, &wb->switch_wbs_ctxs))\n queue_work(isw_wq, &wb->switch_work);\n\nBecause inode_switch_wbs_work_fn() loops when processing isw items, it\ncan happen that wb->switch_work is pending while wb->switch_wbs_ctxs is\nempty. This is a problem because in that case wb can get freed (no isw\nitems -> no wb reference) while the work is still pending causing\nuse-after-free issues.\n\nWe cannot just fix this by cancelling work when freeing wb because that\ncould still trigger problematic 0 -> 1 transitions on wb refcount due to\nwb_get() in inode_switch_wbs_work_fn(). It could be all handled with\nmore careful code but that seems unnecessarily complex so let's avoid\nthat until it is proven that the looping actually brings practical\nbenefit. Just remove the loop from inode_switch_wbs_work_fn() instead.\nThat way when wb_queue_isw() queues work, we are guaranteed we have\nadded the first item to wb->switch_wbs_ctxs and nobody is going to\nremove it (and drop the wb reference it holds) until the queued work\nruns."
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