CVE-2026-98550
En el kernel de Linux se ha resuelto la siguiente vulnerabilidad:
tipc: rechazar GRP_ACK_MSG no válidos e inesperados para evitar el desbordamiento por defecto de bc_ackers
El commit 48a5fe38772b ("tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG") rechazó los ACK duplicados u obsoletos en tipc_group_proto_rcv() devolviendo el control de forma anticipada cuando less_eq(acked, m->bc_acked).
Sin embargo, esa comprobación sigue siendo incompleta de dos formas:
1. Cuando grp->bc_ackers es cero (por ejemplo, en un grupo sin actividad, cuando no se solicitaron los ACK de replicast, o después de que todos los miembros esperados ya hayan confirmado), un GRP_ACK_MSG inesperado con acked > m->bc_acked supera less_eq() y decrementa incondicionalmente grp->bc_ackers. Como bc_ackers es un u16, pasa a 65535, lo que hace que tipc_group_bc_cong() notifique de forma permanente congestión y bloquee todas las futuras difusiones de grupo en el socket.
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2. Durante una ronda de difusión activa (grp->bc_ackers > 0), el emisor transmite el paquete S y avanza grp->bc_snd_nxt a S + 1. Los receptores incrementan su contador esperado a S + 1 al consumir el paquete S, por lo que el único valor de ACK válido para la ronda actual es estrictamente acked == grp->bc_snd_nxt.
No obstante, tipc_group_update_bc_members() inicializa el m->bc_acked de cada miembro a prev = grp->bc_snd_nxt - 1 (S - 1 antes del incremento). Esto deja una brecha de 2 secuencias (de S - 1 a S + 1) en el espacio de secuencias. Por tanto, un ACK entrante no se rechaza como duplicado ni se impide que decremente grp->bc_ackers si llega un valor inesperado o obsoleto (como S). Un miembro que envíe acked = S seguido de acked = S + 1 podría decrementar grp->bc_ackers dos veces en la misma ronda, borrando prematuramente bc_ackers o provocando su desbordamiento.
Para corregirlo: - Descartar GRP_ACK_MSG de inmediato si grp->bc_ackers es cero. - Exigir que acked == grp->bc_snd_nxt y rechazar los duplicados donde m->bc_acked == acked. Como las rondas de difusión replicast son estrictamente secuenciales, solo puede confirmarse grp->bc_snd_nxt, y cada miembro puede confirmar como máximo una vez por ronda.
Cabe señalar que un problema preexistente relacionado en tipc_group_delete_member() (donde la reducción de grp->bc_ackers a cero al abandonar un miembro no restablece *grp->open ni activa el despertar del socket) se abordará en un parche independiente.
Traducción automática del texto original de NVD (en inglés).
CVSS
NVD no ha asignado puntuación CVSS a esta CVE (habitual desde el cambio de política de abril de 2026).
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días
- 0.21 %
- Percentil entre todas las CVEs puntuadas
- 11
- Fecha de la puntuación
- 20/10/2026
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).
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
Mostrar las 8 referencias
- https://git.kernel.org/stable/c/12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b
- https://git.kernel.org/stable/c/478fb08d0c2a53002a721d22b8d6681ec971d90f
- https://git.kernel.org/stable/c/507a27435b2bb1f22e3a3674f6a6553eb815021b
- https://git.kernel.org/stable/c/80a9ccfc24d3776ef6753a57315e726475fac7d7
- https://git.kernel.org/stable/c/99cc2a62e07a44a22254d7beca9ef1f8ad886d0d
- https://git.kernel.org/stable/c/9b94a90651e1fa573c6ac6a5a6b269d5874df2c0
- https://git.kernel.org/stable/c/b0e517961f09b9f60d338d1ea4e17aacdbf206f0
- https://git.kernel.org/stable/c/edc6593c442278fceff0120e8cc58bc592168c35
JSON original (NVD)
Mostrar
{
"id": "CVE-2026-98550",
"cveTags": [],
"metrics": {},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "edc6593c442278fceff0120e8cc58bc592168c35",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "9b94a90651e1fa573c6ac6a5a6b269d5874df2c0",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "507a27435b2bb1f22e3a3674f6a6553eb815021b",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "80a9ccfc24d3776ef6753a57315e726475fac7d7",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "478fb08d0c2a53002a721d22b8d6681ec971d90f",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "b0e517961f09b9f60d338d1ea4e17aacdbf206f0",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "99cc2a62e07a44a22254d7beca9ef1f8ad886d0d",
"versionType": "git"
}
],
"programFiles": [
"net/tipc/group.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "4.15"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "4.15",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.271",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.222",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.189",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.158",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.112",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.55",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.9",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"net/tipc/group.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-10-18T16:17:07.030",
"references": [
{
"url": "https://git.kernel.org/stable/c/12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/478fb08d0c2a53002a721d22b8d6681ec971d90f",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/507a27435b2bb1f22e3a3674f6a6553eb815021b",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/80a9ccfc24d3776ef6753a57315e726475fac7d7",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/99cc2a62e07a44a22254d7beca9ef1f8ad886d0d",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/9b94a90651e1fa573c6ac6a5a6b269d5874df2c0",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/b0e517961f09b9f60d338d1ea4e17aacdbf206f0",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/edc6593c442278fceff0120e8cc58bc592168c35",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow\n\nCommit 48a5fe38772b (\"tipc: fix bc_ackers underflow on duplicate\nGRP_ACK_MSG\") rejected duplicate/stale ACKs in tipc_group_proto_rcv()\nby returning early when less_eq(acked, m->bc_acked).\n\nHowever, that check remains incomplete in two ways:\n\n1. When grp->bc_ackers is zero (e.g. on a quiet group, when replicast\n ACKs were not requested, or after all expected members have already\n acknowledged), an unexpected GRP_ACK_MSG with acked > m->bc_acked\n passes less_eq() and unconditionally decrements grp->bc_ackers.\n Because bc_ackers is a u16, this wraps to 65535, causing\n tipc_group_bc_cong() to permanently report congestion and blocking\n all future group broadcasts on the socket.\n\n2. During an active broadcast round (grp->bc_ackers > 0), the sender\n transmits packet S and advances grp->bc_snd_nxt to S + 1. Receivers\n increment their expected counter to S + 1 upon consuming packet S,\n so the only valid ACK value for the current round is strictly\n acked == grp->bc_snd_nxt.\n\n However, tipc_group_update_bc_members() initializes each member's\n m->bc_acked to prev = grp->bc_snd_nxt - 1 (S - 1 before increment).\n This leaves a 2-sequence gap (S - 1 to S + 1) in sequence space.\n An incoming ACK is therefore neither rejected as duplicate nor\n prevented from decrementing grp->bc_ackers if an unexpected or stale\n value (such as S) is received. A member sending acked = S followed\n by acked = S + 1 could decrement grp->bc_ackers twice in the same\n round, prematurely clearing bc_ackers or underflowing it.\n\nFix this by:\n- Dropping GRP_ACK_MSG immediately if grp->bc_ackers is zero.\n- Requiring acked == grp->bc_snd_nxt and rejecting duplicates where\n m->bc_acked == acked. Because replicast broadcast rounds are strictly\n sequential, only grp->bc_snd_nxt can be acknowledged, and each member\n can acknowledge at most once per round.\n\nNote that a related pre-existing issue in tipc_group_delete_member()\n(where grp->bc_ackers decrementing to zero upon member departure does\nnot restore *grp->open or trigger a socket wakeup) will be addressed\nin a separate patch."
}
],
"lastModified": "2026-10-19T10:19:11.200",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}