{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-31662",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2026-31662"
  ],
  "published": "2026-04-24T14:47:31Z",
  "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.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:12",
        "name": "linux"
      },
      "versions": [
        "1:6.1.47-1+rpt4"
      ],
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-2712",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v6",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v8",
            "binary_version": "1:6.1.47-1+rpt4"
          }
        ]
      },
      "database_specific": {
        "per_version": {
          "1:6.1.47-1+rpt4": {
            "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e",
            "upstream_version": "6.1.47",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.1.169",
            "compiled_filter": false
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-31662"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/a7db57ccca21f5801609065473c89a38229ecb92"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/36ec4fdd6250dcd5e73eb09ea92ed92e9cc28412"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/575faea557f1a184a5f09661bd47ebd3ef3769f8"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/3bcf7aca63f0bcd679ae28e9b99823c608e59ce3"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/a2ea1ef0167d7a84730638d05c20ccdc421b14b6"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/1b6f13f626665cac67ba5a012765427680518711"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/e0bb732eaf77f9ac2f2638bdac9e39b81e0a9682"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/48a5fe38772b6f039522469ee6131a67838221a8"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T13:16:28Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.5,
      "cvss_v3_severity": "High",
      "scenario": "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."
    }
  }
}