Linux Kernel TIPC bc_ackers Underflow Fix
CVE-2026-31662 Published on April 24, 2026
tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG
In the Linux kernel, the following vulnerability has been resolved:
tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG
The GRP_ACK_MSG handler in tipc_group_proto_rcv() currently decrements
bc_ackers on every inbound group ACK, even when the same member has
already acknowledged the current broadcast round.
Because bc_ackers is a u16, a duplicate ACK received after the last
legitimate ACK wraps the counter to 65535. Once wrapped,
tipc_group_bc_cong() keeps reporting congestion and later group
broadcasts on the affected socket stay blocked until the group is
recreated.
Fix this by ignoring duplicate or stale ACKs before touching bc_acked or
bc_ackers. This makes repeated GRP_ACK_MSG handling idempotent and
prevents the underflow path.
Products Associated with CVE-2026-31662
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Affected Versions
Linux:- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below a7db57ccca21f5801609065473c89a38229ecb92 is affected.
- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below 36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412 is affected.
- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below 575faea557f1a184a5f09661bd47ebd3ef3769f8 is affected.
- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below 3bcf7aca63f0bcd679ae28e9b99823c608e59ce3 is affected.
- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below a2ea1ef0167d7a84730638d05c20ccdc421b14b6 is affected.
- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below 1b6f13f626665cac67ba5a012765427680518711 is affected.
- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682 is affected.
- Version 2f487712b89376fce267223bbb0db93d393d4b09 and below 48a5fe38772b6f039522469ee6131a67838221a8 is affected.
- Version 4.15 is affected.
- Before 4.15 is unaffected.
- Version 5.10.253, <= 5.10.* is unaffected.
- Version 5.15.203, <= 5.15.* is unaffected.
- Version 6.1.169, <= 6.1.* is unaffected.
- Version 6.6.135, <= 6.6.* is unaffected.
- Version 6.12.82, <= 6.12.* is unaffected.
- Version 6.18.23, <= 6.18.* is unaffected.
- Version 6.19.13, <= 6.19.* is unaffected.
- Version 7.0, <= * is unaffected.