{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-98550", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.356Z", "datePublished": "2026-10-18T15:18:18.173Z", "dateUpdated": "2026-10-19T09:21:33.349Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T09:21:33.349Z" }, "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." } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/tipc/group.c" ], "versions": [ { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "edc6593c442278fceff0120e8cc58bc592168c35", "status": "affected", "versionType": "git" }, { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "9b94a90651e1fa573c6ac6a5a6b269d5874df2c0", "status": "affected", "versionType": "git" }, { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "507a27435b2bb1f22e3a3674f6a6553eb815021b", "status": "affected", "versionType": "git" }, { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "80a9ccfc24d3776ef6753a57315e726475fac7d7", "status": "affected", "versionType": "git" }, { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "478fb08d0c2a53002a721d22b8d6681ec971d90f", "status": "affected", "versionType": "git" }, { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b", "status": "affected", "versionType": "git" }, { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "b0e517961f09b9f60d338d1ea4e17aacdbf206f0", "status": "affected", "versionType": "git" }, { "version": "2f487712b89376fce267223bbb0db93d393d4b09", "lessThan": "99cc2a62e07a44a22254d7beca9ef1f8ad886d0d", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/tipc/group.c" ], "versions": [ { "version": "4.15", "status": "affected" }, { "version": "0", "lessThan": "4.15", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.271", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.222", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.189", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.158", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.112", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.55", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.9", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "5.10.271" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "5.15.222" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "6.1.189" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "6.6.158" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "6.12.112" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "6.18.55" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "7.2.9" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.15", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/edc6593c442278fceff0120e8cc58bc592168c35" }, { "url": "https://git.kernel.org/stable/c/9b94a90651e1fa573c6ac6a5a6b269d5874df2c0" }, { "url": "https://git.kernel.org/stable/c/507a27435b2bb1f22e3a3674f6a6553eb815021b" }, { "url": "https://git.kernel.org/stable/c/80a9ccfc24d3776ef6753a57315e726475fac7d7" }, { "url": "https://git.kernel.org/stable/c/478fb08d0c2a53002a721d22b8d6681ec971d90f" }, { "url": "https://git.kernel.org/stable/c/12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b" }, { "url": "https://git.kernel.org/stable/c/b0e517961f09b9f60d338d1ea4e17aacdbf206f0" }, { "url": "https://git.kernel.org/stable/c/99cc2a62e07a44a22254d7beca9ef1f8ad886d0d" } ], "title": "tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow", "x_generator": { "engine": "bippy-1.2.0" } } } }