{"id":"CVE-2026-31662","summary":"tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG","details":"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, 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.","modified":"2026-07-09T18:30:29.229802313Z","published":"2026-04-24T14:45:12.593Z","related":["SUSE-SU-2026:2111-1","SUSE-SU-2026:21834-1","SUSE-SU-2026:21841-1","SUSE-SU-2026:21845-1","SUSE-SU-2026:21860-1","SUSE-SU-2026:21876-1","SUSE-SU-2026:21877-1","SUSE-SU-2026:21916-1","SUSE-SU-2026:21919-1","SUSE-SU-2026:2195-1","SUSE-SU-2026:2202-1","SUSE-SU-2026:2215-1","SUSE-SU-2026:2216-1","SUSE-SU-2026:2217-1","SUSE-SU-2026:2238-1","openSUSE-SU-2026:20826-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31662.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/1b6f13f626665cac67ba5a012765427680518711"},{"type":"WEB","url":"https://git.kernel.org/stable/c/36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412"},{"type":"WEB","url":"https://git.kernel.org/stable/c/3bcf7aca63f0bcd679ae28e9b99823c608e59ce3"},{"type":"WEB","url":"https://git.kernel.org/stable/c/48a5fe38772b6f039522469ee6131a67838221a8"},{"type":"WEB","url":"https://git.kernel.org/stable/c/575faea557f1a184a5f09661bd47ebd3ef3769f8"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a2ea1ef0167d7a84730638d05c20ccdc421b14b6"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a7db57ccca21f5801609065473c89a38229ecb92"},{"type":"WEB","url":"https://git.kernel.org/stable/c/e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31662.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31662"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"2f487712b89376fce267223bbb0db93d393d4b09"},{"fixed":"a7db57ccca21f5801609065473c89a38229ecb92"},{"fixed":"36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412"},{"fixed":"575faea557f1a184a5f09661bd47ebd3ef3769f8"},{"fixed":"3bcf7aca63f0bcd679ae28e9b99823c608e59ce3"},{"fixed":"a2ea1ef0167d7a84730638d05c20ccdc421b14b6"},{"fixed":"1b6f13f626665cac67ba5a012765427680518711"},{"fixed":"e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682"},{"fixed":"48a5fe38772b6f039522469ee6131a67838221a8"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31662.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"4.15.0"},{"fixed":"5.10.253"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"5.15.203"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.16.0"},{"fixed":"6.1.169"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.135"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.82"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.23"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.13"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-31662.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}