CVE-2026-31662 (GCVE-0-2026-31662)
Vulnerability from cvelistv5
Published
2026-04-24 14:45
Modified
2026-08-05 12:24
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/tipc/group.c"
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              "version": "0",
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              "status": "unaffected",
              "version": "7.0",
              "versionType": "original_commit_for_fix"
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        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "cpeMatch": [
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              "negate": false,
              "operator": "OR"
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        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable handler processes TIPC GROUP_PROTOCOL messages received over configured TIPC bearers, including UDP/IP bearers that accept network packets from peer nodes. A malicious remote TIPC peer can send crafted or duplicate GRP_ACK_MSG packets to the victim group socket.\nAC:L - There is no race or hard-to-control condition; after joining or appearing as a group member, the attacker can send an ACK and then a stale or duplicate ACK with a new link sequence number. The triggering state is a normal replicast group broadcast with ACKs enabled.\nPR:N - The attacker does not need privileges on the victim system; TIPC discovery/group protocol messages are accepted from network peers after normal bearer/node establishment, with no mandatory authentication in the vulnerable path. Optional TIPC crypto or deployment filtering is not required for the vulnerable code path.\nUI:N - No victim user action is required once the vulnerable TIPC group service is running. The attacker triggers the bug by sending network protocol messages.\nS:U - The impact remains within the same kernel/TIPC communication security authority. There is no VM escape, sandbox escape, or cross-authority boundary bypass.\nC:N - The bug is a logical u16 counter underflow in group broadcast ACK accounting, not a memory disclosure or memory corruption primitive. It does not provide a way to read confidential data.\nI:N - The attacker corrupts protocol accounting state only to block later broadcasts; there is no unauthorized data modification, arbitrary write, or control-flow impact. The security consequence is denial of service rather than integrity compromise.\nA:H - Wrapping bc_ackers to 65535 makes tipc_group_bc_cong() keep reporting congestion, so subsequent group broadcasts on the affected socket remain blocked until the group is recreated. In a TIPC-based clustered or control deployment this is a persistent, remotely triggerable loss of availability for the affected communication channel."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:24:12.893Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "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"
        }
      ],
      "title": "tipc: fix bc_ackers underflow on duplicate GRP_ACK_MSG",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-31662",
    "datePublished": "2026-04-24T14:45:12.593Z",
    "dateReserved": "2026-03-09T15:48:24.129Z",
    "dateUpdated": "2026-08-05T12:24:12.893Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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