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tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow

Type: advisorySource: Official CVE List1 source record

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 =

Announced Source revision 1
Original source ↗

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
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Publisher date
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