264 lines
15 KiB
JSON
264 lines
15 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-98550",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2026-09-25T10:25:14.356Z",
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"datePublished": "2026-10-18T15:18:18.173Z",
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"dateUpdated": "2026-10-24T14:09:23.470Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-10-24T14:09:23.470Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"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."
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
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"baseScore": 7.5,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:N - A crafted UDP/IP TIPC GROUP_PROTOCOL/GRP_ACK_MSG carrying attacker-controlled msg_grp_bc_acked() reaches tipc_group_proto_rcv() through tipc_udp_recv(), tipc_rcv(), link delivery, and socket filtering. The UDP bearer is routable.\nAC:L - After becoming a recognized group member, the attacker can send one ACK that compares newer than m->bc_acked while grp->bc_ackers is zero, deterministically causing the underflow. No race or external condition is required.\nPR:N - The GRP_ACK_MSG case in tipc_group_proto_rcv() verifies only that the packet's origin node and port match a tipc_member; it performs no credential or capability check. TIPC wire encryption is optional, so no victim-system privilege is required.\nUI:N - Once a cluster-scope TIPC group socket exists, the remote member triggers tipc_group_proto_rcv() solely by sending the crafted GRP_ACK_MSG; no victim action is needed.\nS:U - The malformed ACK changes grp->bc_ackers and availability of the same kernel-managed TIPC group socket; it does not cross a VM, sandbox, or other security-authority boundary.\nC:N - The faulty operation is a decrement of the u16 grp->bc_ackers field from zero to 65535. It neither reads outside an object nor returns kernel or application data to the sender.\nI:N - The bug alters only TIPC ACK-accounting state through the intended grp->bc_ackers field; it provides no out-of-bounds write, control-flow primitive, or modification of application data.\nA:H - After grp->bc_ackers wraps to 65535, tipc_group_bc_cong() continually reports congestion and tipc_send_group_bcast() blocks or fails all later broadcasts on that socket until the group is recreated."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"net/tipc/group.c"
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],
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"versions": [
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{
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"status": "affected",
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"lessThan": "12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b",
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"status": "affected",
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"status": "affected",
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"lessThan": "99cc2a62e07a44a22254d7beca9ef1f8ad886d0d",
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"status": "affected",
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}
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]
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},
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "affected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"net/tipc/group.c"
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],
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"versions": [
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{
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"version": "4.15",
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"status": "affected"
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},
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{
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"version": "0",
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"lessThan": "4.15",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "5.10.271",
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"lessThanOrEqual": "5.10.*",
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"status": "unaffected",
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},
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{
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"version": "5.15.222",
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"lessThanOrEqual": "5.15.*",
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"status": "unaffected",
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},
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{
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"version": "6.1.189",
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"lessThanOrEqual": "6.1.*",
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"status": "unaffected",
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},
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{
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"version": "6.6.158",
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"lessThanOrEqual": "6.6.*",
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"status": "unaffected",
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},
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{
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"version": "6.12.112",
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"lessThanOrEqual": "6.12.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.18.55",
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"lessThanOrEqual": "6.18.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.2.9",
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"lessThanOrEqual": "7.2.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.3",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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"cpeApplicability": [
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},
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},
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"url": "https://git.kernel.org/stable/c/478fb08d0c2a53002a721d22b8d6681ec971d90f"
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"url": "https://git.kernel.org/stable/c/12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b"
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{
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},
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{
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"url": "https://git.kernel.org/stable/c/99cc2a62e07a44a22254d7beca9ef1f8ad886d0d"
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}
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],
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"title": "tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow",
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"x_generator": {
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"engine": "bippy-1.2.0"
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}
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} |