tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow
In the Linux kernel, the following vulnerability has been resolved: tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow Commit 48a5fe38772b ("tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG") rejected duplicate/stale ACKs in tipc_group_proto_rcv() by returning early when less_eq(acked, m->bc_acked). However, that check remains incomplete in two ways: 1. When grp->bc_ackers is zero (e.g. on a quiet group, when replicast ACKs were not requested, or after all expected members have already acknowledged), an unexpected GRP_ACK_MSG with acked > m->bc_acked passes less_eq() and unconditionally decrements grp->bc_ackers. Because bc_ackers is a u16, this wraps to 65535, causing tipc_group_bc_cong() to permanently report congestion and blocking all future group broadcasts on the socket. 2. During an active broadcast round (grp->bc_ackers > 0), the sender transmits packet S and advances grp->bc_snd_nxt to S + 1. Receivers increment their expected counter to S + 1 upon consuming packet S, so the only valid ACK value for the current round is strictly acked == grp->bc_snd_nxt. However, tipc_group_update_bc_members() initializes each member's m->bc_acked to prev = grp->bc_snd_nxt - 1 (S - 1 before increment). This leaves a 2-sequence gap (S - 1 to S + 1) in sequence space. An incoming ACK is therefore neither rejected as duplicate nor prevented from decrementing grp->bc_ackers if an unexpected or stale value (such as S) is received. A member sending acked =
CVE-2026-98550
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-98550
Linux
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Linux
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "edc6593c442278fceff0120e8cc58bc592168c35",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "9b94a90651e1fa573c6ac6a5a6b269d5874df2c0",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "507a27435b2bb1f22e3a3674f6a6553eb815021b",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "80a9ccfc24d3776ef6753a57315e726475fac7d7",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "478fb08d0c2a53002a721d22b8d6681ec971d90f",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "b0e517961f09b9f60d338d1ea4e17aacdbf206f0",
"versionType": "git"
},
{
"status": "affected",
"version": "2f487712b89376fce267223bbb0db93d393d4b09",
"lessThan": "99cc2a62e07a44a22254d7beca9ef1f8ad886d0d",
"versionType": "git"
}
],
"programFiles": [
"net/tipc/group.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "4.15"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "4.15",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.271",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.222",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.189",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.158",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.112",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.55",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.9",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"net/tipc/group.c"
],
"defaultStatus": "affected"
}
]- Related CVEs
- CVE-2026-98550
Source reference:
/cveMetadata/cveId
Publisher severity
high
Source reference: /containers/cna/metrics
- Event
- #55616 · Revision 1
- Added to Heist Feed
- Publisher date