{"id":"CVE-2026-31662","title":"tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG\n\nThe GRP_ACK_MSG handler in tipc_group_proto_rcv() currently decrements\nbc_ackers on every inbound group ACK, eve…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < a7db57ccca21f5801609065473c89a38229ecb92","Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412","Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 575faea557f1a184a5f09661bd47ebd3ef3769f8","Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 3bcf7aca63f0bcd679ae28e9b99823c608e59ce3","Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < a2ea1ef0167d7a84730638d05c20ccdc421b14b6","Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 1b6f13f626665cac67ba5a012765427680518711","Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682","Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 48a5fe38772b6f039522469ee6131a67838221a8","Linux 4.15"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-10-16T15:11:44.605157Z"},"published":"2026-04-24","updated":"2026-10-16","sourceUpdated":"2026-10-16T15:20:20.659Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31662","references":[{"url":"https://git.kernel.org/stable/c/a7db57ccca21f5801609065473c89a38229ecb92"},{"url":"https://git.kernel.org/stable/c/36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412"},{"url":"https://git.kernel.org/stable/c/575faea557f1a184a5f09661bd47ebd3ef3769f8"},{"url":"https://git.kernel.org/stable/c/3bcf7aca63f0bcd679ae28e9b99823c608e59ce3"},{"url":"https://git.kernel.org/stable/c/a2ea1ef0167d7a84730638d05c20ccdc421b14b6"},{"url":"https://git.kernel.org/stable/c/1b6f13f626665cac67ba5a012765427680518711"},{"url":"https://git.kernel.org/stable/c/e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682"},{"url":"https://git.kernel.org/stable/c/48a5fe38772b6f039522469ee6131a67838221a8"}],"tags":["cve.org"],"epss":0.00389,"epssPercentile":0.31392,"ingestedAt":"2026-10-16T17:24:46.667Z","slug":"CVE-2026-31662","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\ntipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG\n\nThe GRP_ACK_MSG handler in tipc_group_proto_rcv() currently decrements\nbc_ackers on every inbound group ACK, even when the same member has\nalready acknowledged the current broadcast round.\n\nBecause bc_ackers is a u16, a duplicate ACK received after the last\nlegitimate ACK wraps the counter to 65535. Once wrapped,\ntipc_group_bc_cong() keeps reporting congestion and later group\nbroadcasts on the affected socket stay blocked until the group is\nrecreated.\n\nFix this by ignoring duplicate or stale ACKs before touching bc_acked or\nbc_ackers. This makes repeated GRP_ACK_MSG handling idempotent and\nprevents the underflow path.\n\n## Affected\n\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < a7db57ccca21f5801609065473c89a38229ecb92`\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412`\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 575faea557f1a184a5f09661bd47ebd3ef3769f8`\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 3bcf7aca63f0bcd679ae28e9b99823c608e59ce3`\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < a2ea1ef0167d7a84730638d05c20ccdc421b14b6`\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 1b6f13f626665cac67ba5a012765427680518711`\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682`\n- `Linux >= 2f487712b89376fce267223bbb0db93d393d4b09 < 48a5fe38772b6f039522469ee6131a67838221a8`\n- `Linux 4.15`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}