CVE-2026-46242
Full vulnerability record from the local CVENow database.
Description
In the Linux kernel, the following vulnerability has been resolved: eventpoll: fix ep_remove struct eventpoll / struct file UAF ep_remove() (via ep_remove_file()) cleared file->f_ep under file->f_lock but then kept using @file inside the critical section (is_file_epoll(), hlist_del_rcu() through the head, spin_unlock). A concurrent __fput() taking the eventpoll_release() fastpath in that window observed the transient NULL, skipped eventpoll_release_file() and ran to f_op->release / file_free(). For the epoll-watches-epoll case, f_op->release is ep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), which kfree()s the watched struct eventpoll. Its embedded ->refs hlist_head is exactly where epi->fllink.pprev points, so the subsequent hlist_del_rcu()'s "*pprev = next" scribbles into freed kmalloc-192 memory. In addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slot backing @file could be recycled by alloc_empty_file() -- reinitializing f_lock and f_ep -- while ep_remove() is still nominally inside that lock. The upshot is an attacker-controllable kmem_cache_free() against the wrong slab cache. Pin @file via epi_fget() at the top of ep_remove() and gate the critical section on the pin succeeding. With the pin held @file cannot reach refcount zero, which holds __fput() off and transitively keeps the watched struct eventpoll alive across the hlist_del_rcu() and the f_lock use, closing both UAFs. If the pin fails @file has already reached refcount zero and its __fput() is in flight. Because we bailed before clearing f_ep, that path takes the eventpoll_release() slow path into eventpoll_release_file() and blocks on ep->mtx until the waiter side's ep_clear_and_put() drops it. The bailed epi's share of ep->refcount stays intact, so the trailing ep_refcount_dec_and_test() in ep_clear_and_put() cannot free the eventpoll out from under eventpoll_release_file(); the orphaned epi is then cleaned up there. A successful pin also proves we are not racing eventpoll_release_file() on this epi, so drop the now-redundant re-check of epi->dying under f_lock. The cheap lockless READ_ONCE(epi->dying) fast-path bailout stays.
Severity
HIGH
CVSS score
7.8
(v3.1)
Vulnerability status
Modified
Source identifier
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Published
2026-05-30 13:16:21.980000
Last modified
2026-10-19 20:18:39.123000
View original CVE JSON
{
"id": "CVE-2026-46242",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"published": "2026-05-30T13:16:21.980",
"lastModified": "2026-10-19T20:18:39.123",
"vulnStatus": "Modified",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\neventpoll: fix ep_remove struct eventpoll / struct file UAF\n\nep_remove() (via ep_remove_file()) cleared file->f_ep under\nfile->f_lock but then kept using @file inside the critical section\n(is_file_epoll(), hlist_del_rcu() through the head, spin_unlock).\nA concurrent __fput() taking the eventpoll_release() fastpath in\nthat window observed the transient NULL, skipped\neventpoll_release_file() and ran to f_op->release / file_free().\n\nFor the epoll-watches-epoll case, f_op->release is\nep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), which\nkfree()s the watched struct eventpoll. Its embedded ->refs\nhlist_head is exactly where epi->fllink.pprev points, so the\nsubsequent hlist_del_rcu()'s \"*pprev = next\" scribbles into freed\nkmalloc-192 memory.\n\nIn addition, struct file is SLAB_TYPESAFE_BY_RCU, so the slot\nbacking @file could be recycled by alloc_empty_file() --\nreinitializing f_lock and f_ep -- while ep_remove() is still\nnominally inside that lock. The upshot is an attacker-controllable\nkmem_cache_free() against the wrong slab cache.\n\nPin @file via epi_fget() at the top of ep_remove() and gate the\ncritical section on the pin succeeding. With the pin held @file\ncannot reach refcount zero, which holds __fput() off and\ntransitively keeps the watched struct eventpoll alive across the\nhlist_del_rcu() and the f_lock use, closing both UAFs.\n\nIf the pin fails @file has already reached refcount zero and its\n__fput() is in flight. Because we bailed before clearing f_ep,\nthat path takes the eventpoll_release() slow path into\neventpoll_release_file() and blocks on ep->mtx until the waiter\nside's ep_clear_and_put() drops it. The bailed epi's share of\nep->refcount stays intact, so the trailing ep_refcount_dec_and_test()\nin ep_clear_and_put() cannot free the eventpoll out from under\neventpoll_release_file(); the orphaned epi is then cleaned up\nthere.\n\nA successful pin also proves we are not racing\neventpoll_release_file() on this epi, so drop the now-redundant\nre-check of epi->dying under f_lock. The cheap lockless\nREAD_ONCE(epi->dying) fast-path bailout stays."
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\neventpoll: corrección de UAF de struct eventpoll / struct file en ep_remove\n\nep_remove() (a través de ep_remove_file()) limpió file->f_ep bajo file->f_lock pero luego siguió usando @file dentro de la sección crítica (is_file_epoll(), hlist_del_rcu() a través del encabezado, spin_unlock). Un __fput() concurrente que tomaba la ruta rápida de eventpoll_release() en esa ventana observó el NULL transitorio, omitió eventpoll_release_file() y se ejecutó a f_op->release / file_free().\n\nPara el caso de epoll-observa-epoll, f_op->release es ep_eventpoll_release() -> ep_clear_and_put() -> ep_free(), que libera con kfree() la struct eventpoll observada. Su hlist_head ->refs incrustada es exactamente donde apunta epi->fllink.pprev, por lo que el \"*pprev = next\" del hlist_del_rcu() subsiguiente escribe en memoria kmalloc-192 liberada.\n\nAdemás, struct file es SLAB_TYPESAFE_BY_RCU, por lo que el slot que respalda a @file podría ser reciclado por alloc_empty_file() -- reinicializando f_lock y f_ep -- mientras ep_remove() todavía está nominalmente dentro de ese bloqueo. El resultado es un kmem_cache_free() controlable por un atacante contra la caché de slab incorrecta.\n\nFija @file a través de epi_fget() al inicio de ep_remove() y condiciona la sección crítica al éxito de la fijación. Con la fijación mantenida, @file no puede alcanzar un recuento de referencias de cero, lo que evita que __fput() se ejecute y mantiene transitivamente viva la struct eventpoll observada a través del hlist_del_rcu() y el uso de f_lock, cerrando ambas UAFs.\n\nSi la fijación falla, @file ya ha alcanzado un recuento de referencias de cero y su __fput() está en curso. Debido a que abortamos antes de limpiar f_ep, esa ruta toma la ruta lenta de eventpoll_release() hacia eventpoll_release_file() y se bloquea en ep->mtx hasta que el ep_clear_and_put() del lado del esperador lo suelta. La parte de ep->refcount del epi abortado permanece intacta, por lo que el ep_refcount_dec_and_test() final en ep_clear_and_put() no puede liberar el eventpoll por debajo de eventpoll_release_file(); el epi huérfano es entonces limpiado allí.\n\nUna fijación exitosa también prueba que no estamos compitiendo con eventpoll_release_file() en este epi, por lo que se elimina la ahora redundante nueva verificación de epi->dying bajo f_lock. La salida rápida barata sin bloqueo de READ_ONCE(epi->dying) permanece."
}
],
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "unaffected",
"programFiles": [
"fs/eventpoll.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "f2451def095c1743adcfcb0cb5dadc86034e162a",
"lessThan": "a10fbbe74e1c743beb1bb312109366667461df8a",
"versionType": "git",
"status": "affected"
},
{
"version": "a1f93804449d13f97dabd4b996817de4bf1ed67a",
"lessThan": "3e1144d2515d28e4312e663ea05eac203101491d",
"versionType": "git",
"status": "affected"
},
{
"version": "58c9b016e12855286370dfb704c08498edbc857a",
"lessThan": "2de4db145b2992da496fea6c51f9839be678ae24",
"versionType": "git",
"status": "affected"
},
{
"version": "58c9b016e12855286370dfb704c08498edbc857a",
"lessThan": "9324de74a3a59b9fde9b62ee45ebaa71458ba2e5",
"versionType": "git",
"status": "affected"
},
{
"version": "58c9b016e12855286370dfb704c08498edbc857a",
"lessThan": "ef4ca02e95363e78977ca04340d44fe3b4b2b81f",
"versionType": "git",
"status": "affected"
},
{
"version": "58c9b016e12855286370dfb704c08498edbc857a",
"lessThan": "ced39b6a8062bac5c18a1c3df85634107eb8664a",
"versionType": "git",
"status": "affected"
},
{
"version": "58c9b016e12855286370dfb704c08498edbc857a",
"lessThan": "a6dc643c69311677c574a0f17a3f4d66a5f3744b",
"versionType": "git",
"status": "affected"
},
{
"version": "5.15.209",
"lessThan": "5.15.222",
"versionType": "semver",
"status": "affected"
},
{
"version": "6.1.175",
"lessThan": "6.1.178",
"versionType": "semver",
"status": "affected"
}
]
},
{
"vendor": "Linux",
"product": "Linux",
"defaultStatus": "affected",
"programFiles": [
"fs/eventpoll.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"versions": [
{
"version": "6.4",
"status": "affected"
},
{
"version": "0",
"lessThan": "6.4",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "5.15.222",
"lessThanOrEqual": "5.15.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.1.178",
"lessThanOrEqual": "6.1.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.6.144",
"lessThanOrEqual": "6.6.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.12.95",
"lessThanOrEqual": "6.12.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "6.18.33",
"lessThanOrEqual": "6.18.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.0.10",
"lessThanOrEqual": "7.0.*",
"versionType": "semver",
"status": "unaffected"
},
{
"version": "7.1",
"lessThanOrEqual": "*",
"versionType": "original_commit_for_fix",
"status": "unaffected"
}
]
}
]
}
],
"metrics": {
"cvssMetricV31": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary",
"cvssData": {
"version": "3.1",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"attackVector": "LOCAL",
"attackComplexity": "LOW",
"privilegesRequired": "LOW",
"userInteraction": "NONE",
"scope": "UNCHANGED",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"availabilityImpact": "HIGH"
},
"exploitabilityScore": 1.8,
"impactScore": 5.9
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"timestamp": "2026-10-16T15:21:18.370364Z",
"id": "CVE-2026-46242",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"version": "2.0.3"
}
}
]
},
"weaknesses": [
{
"source": "[email protected]",
"type": "Primary",
"description": [
{
"lang": "en",
"value": "CWE-416"
}
]
},
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"type": "Secondary",
"description": [
{
"lang": "en",
"value": "CWE-416"
}
]
}
],
"configurations": [
{
"nodes": [
{
"operator": "OR",
"negate": false,
"cpeMatch": [
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "5.15.209",
"versionEndExcluding": "5.16",
"matchCriteriaId": "DA466B5F-044E-47F0-A6CE-AB474F8A9361"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "6.1.175",
"versionEndExcluding": "6.2",
"matchCriteriaId": "67892698-2698-487E-B4D2-EFCD2D933D19"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "6.4",
"versionEndExcluding": "6.18.33",
"matchCriteriaId": "51601BBF-BF40-48AF-8132-2582D7E56D71"
},
{
"vulnerable": true,
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionStartIncluding": "6.19",
"versionEndExcluding": "7.0.10",
"matchCriteriaId": "A13475D2-59BF-4716-94B5-7C1D239A2CF4"
}
]
}
]
}
],
"references": [
{
"url": "https://git.kernel.org/stable/c/2de4db145b2992da496fea6c51f9839be678ae24",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/3e1144d2515d28e4312e663ea05eac203101491d",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/9324de74a3a59b9fde9b62ee45ebaa71458ba2e5",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/a10fbbe74e1c743beb1bb312109366667461df8a",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/a6dc643c69311677c574a0f17a3f4d66a5f3744b",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
]
},
{
"url": "https://git.kernel.org/stable/c/ced39b6a8062bac5c18a1c3df85634107eb8664a",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
]
},
{
"url": "https://git.kernel.org/stable/c/ef4ca02e95363e78977ca04340d44fe3b4b2b81f",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"tags": [
"Patch"
]
},
{
"url": "http://www.openwall.com/lists/oss-security/2026/07/08/14",
"source": "af854a3a-2127-422b-91ae-364da2661108"
}
]
}