CVE-2026-46242 (GCVE-0-2026-46242)
Vulnerability from cvelistv5 – Published: 2026-05-30 12:13 – Updated: 2026-10-03 10:55
VLAI
EPSS
VEX
Title
eventpoll: fix ep_remove struct eventpoll / struct file UAF
Summary
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
7.8 (High)
Assigner
References
8 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
f2451def095c1743adcfcb0cb5dadc86034e162a , < a10fbbe74e1c743beb1bb312109366667461df8a
(git)
Affected: a1f93804449d13f97dabd4b996817de4bf1ed67a , < 3e1144d2515d28e4312e663ea05eac203101491d (git) Affected: 58c9b016e12855286370dfb704c08498edbc857a , < 2de4db145b2992da496fea6c51f9839be678ae24 (git) Affected: 58c9b016e12855286370dfb704c08498edbc857a , < 9324de74a3a59b9fde9b62ee45ebaa71458ba2e5 (git) Affected: 58c9b016e12855286370dfb704c08498edbc857a , < ef4ca02e95363e78977ca04340d44fe3b4b2b81f (git) Affected: 58c9b016e12855286370dfb704c08498edbc857a , < ced39b6a8062bac5c18a1c3df85634107eb8664a (git) Affected: 58c9b016e12855286370dfb704c08498edbc857a , < a6dc643c69311677c574a0f17a3f4d66a5f3744b (git) Affected: 5.15.209 , < 5.15.222 (semver) Affected: 6.1.175 , < 6.1.178 (semver) |
guessed | |
| Linux | Linux |
Affected:
6.4
Unaffected: 0 , < 6.4 (semver) Unaffected: 5.15.222 , ≤ 5.15.* (semver) Unaffected: 6.1.178 , ≤ 6.1.* (semver) Unaffected: 6.6.144 , ≤ 6.6.* (semver) Unaffected: 6.12.95 , ≤ 6.12.* (semver) Unaffected: 6.18.33 , ≤ 6.18.* (semver) Unaffected: 7.0.10 , ≤ 7.0.* (semver) Unaffected: 7.1 , ≤ * (original_commit_for_fix) |
guessed |
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"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-\u003ef_ep under\nfile-\u003ef_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-\u003erelease / file_free().\n\nFor the epoll-watches-epoll case, f_op-\u003erelease is\nep_eventpoll_release() -\u003e ep_clear_and_put() -\u003e ep_free(), which\nkfree()s the watched struct eventpoll. Its embedded -\u003erefs\nhlist_head is exactly where epi-\u003efllink.pprev points, so the\nsubsequent hlist_del_rcu()\u0027s \"*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-\u003emtx until the waiter\nside\u0027s ep_clear_and_put() drops it. The bailed epi\u0027s share of\nep-\u003erefcount 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-\u003edying under f_lock. The cheap lockless\nREAD_ONCE(epi-\u003edying) fast-path bailout stays."
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{
"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-\u003ef_ep under\nfile-\u003ef_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-\u003erelease / file_free().\n\nFor the epoll-watches-epoll case, f_op-\u003erelease is\nep_eventpoll_release() -\u003e ep_clear_and_put() -\u003e ep_free(), which\nkfree()s the watched struct eventpoll. Its embedded -\u003erefs\nhlist_head is exactly where epi-\u003efllink.pprev points, so the\nsubsequent hlist_del_rcu()\u0027s \"*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-\u003emtx until the waiter\nside\u0027s ep_clear_and_put() drops it. The bailed epi\u0027s share of\nep-\u003erefcount 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-\u003edying under f_lock. The cheap lockless\nREAD_ONCE(epi-\u003edying) fast-path bailout stays."
},
{
"lang": "es",
"value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\neventpoll: correcci\u00f3n de UAF de struct eventpoll / struct file en ep_remove\n\nep_remove() (a trav\u00e9s de ep_remove_file()) limpi\u00f3 file-\u003ef_ep bajo file-\u003ef_lock pero luego sigui\u00f3 usando @file dentro de la secci\u00f3n cr\u00edtica (is_file_epoll(), hlist_del_rcu() a trav\u00e9s del encabezado, spin_unlock). Un __fput() concurrente que tomaba la ruta r\u00e1pida de eventpoll_release() en esa ventana observ\u00f3 el NULL transitorio, omiti\u00f3 eventpoll_release_file() y se ejecut\u00f3 a f_op-\u003erelease / file_free().\n\nPara el caso de epoll-observa-epoll, f_op-\u003erelease es ep_eventpoll_release() -\u003e ep_clear_and_put() -\u003e ep_free(), que libera con kfree() la struct eventpoll observada. Su hlist_head -\u003erefs incrustada es exactamente donde apunta epi-\u003efllink.pprev, por lo que el \"*pprev = next\" del hlist_del_rcu() subsiguiente escribe en memoria kmalloc-192 liberada.\n\nAdem\u00e1s, struct file es SLAB_TYPESAFE_BY_RCU, por lo que el slot que respalda a @file podr\u00eda ser reciclado por alloc_empty_file() -- reinicializando f_lock y f_ep -- mientras ep_remove() todav\u00eda est\u00e1 nominalmente dentro de ese bloqueo. El resultado es un kmem_cache_free() controlable por un atacante contra la cach\u00e9 de slab incorrecta.\n\nFija @file a trav\u00e9s de epi_fget() al inicio de ep_remove() y condiciona la secci\u00f3n cr\u00edtica al \u00e9xito de la fijaci\u00f3n. Con la fijaci\u00f3n 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 trav\u00e9s del hlist_del_rcu() y el uso de f_lock, cerrando ambas UAFs.\n\nSi la fijaci\u00f3n falla, @file ya ha alcanzado un recuento de referencias de cero y su __fput() est\u00e1 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-\u003emtx hasta que el ep_clear_and_put() del lado del esperador lo suelta. La parte de ep-\u003erefcount 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 hu\u00e9rfano es entonces limpiado all\u00ed.\n\nUna fijaci\u00f3n exitosa tambi\u00e9n prueba que no estamos compitiendo con eventpoll_release_file() en este epi, por lo que se elimina la ahora redundante nueva verificaci\u00f3n de epi-\u003edying bajo f_lock. La salida r\u00e1pida barata sin bloqueo de READ_ONCE(epi-\u003edying) permanece."
}
],
"id": "CVE-2026-46242",
"lastModified": "2026-10-03T11:17:34.837",
"metrics": {
"cvssMetricV31": [
{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.8,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "HIGH",
"privilegesRequired": "LOW",
"scope": "UNCHANGED",
"userInteraction": "NONE",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"version": "3.1"
},
"exploitabilityScore": 1.8,
"impactScore": 5.9,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
]
},
"published": "2026-05-30T13:16:21.980",
"references": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"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",
"tags": [
"Patch"
],
"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": "af854a3a-2127-422b-91ae-364da2661108",
"url": "http://www.openwall.com/lists/oss-security/2026/07/08/14"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Modified",
"weaknesses": [
{
"description": [
{
"lang": "en",
"value": "CWE-416"
}
],
"source": "nvd@nist.gov",
"type": "Primary"
}
]
}
},
"redhat_vex": {
"aggregate_severity": "Important",
"current_release_date": "2026-10-13T13:50:33+00:00",
"cve": "CVE-2026-46242",
"id": "CVE-2026-46242",
"initial_release_date": "2026-05-30T00:00:00+00:00",
"product_status:fixed": "1656",
"product_status:known_affected": "1",
"product_status:known_not_affected": "112",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: eventpoll: fix ep_remove struct eventpoll / struct file UAF",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-46242.json",
"version": "3"
}
}
}
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Sightings
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Nomenclature
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
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They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
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