CVE-2026-98550 (GCVE-0-2026-98550)
Vulnerability from cvelistv5
Published
2026-10-18 15:18
Modified
2026-10-24 14:09
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: 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 = S followed by acked = S + 1 could decrement grp->bc_ackers twice in the same round, prematurely clearing bc_ackers or underflowing it. Fix this by: - Dropping GRP_ACK_MSG immediately if grp->bc_ackers is zero. - Requiring acked == grp->bc_snd_nxt and rejecting duplicates where m->bc_acked == acked. Because replicast broadcast rounds are strictly sequential, only grp->bc_snd_nxt can be acknowledged, and each member can acknowledge at most once per round. Note that a related pre-existing issue in tipc_group_delete_member() (where grp->bc_ackers decrementing to zero upon member departure does not restore *grp->open or trigger a socket wakeup) will be addressed in a separate patch.
References
Impacted products
Vendor Product Version
Linux Linux Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
Version: 2f487712b89376fce267223bbb0db93d393d4b09
 Create a notification for this product.
Show details on NVD website

To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/tipc/group.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "edc6593c442278fceff0120e8cc58bc592168c35",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            },
            {
              "lessThan": "9b94a90651e1fa573c6ac6a5a6b269d5874df2c0",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            },
            {
              "lessThan": "507a27435b2bb1f22e3a3674f6a6553eb815021b",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            },
            {
              "lessThan": "80a9ccfc24d3776ef6753a57315e726475fac7d7",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            },
            {
              "lessThan": "478fb08d0c2a53002a721d22b8d6681ec971d90f",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            },
            {
              "lessThan": "12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            },
            {
              "lessThan": "b0e517961f09b9f60d338d1ea4e17aacdbf206f0",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            },
            {
              "lessThan": "99cc2a62e07a44a22254d7beca9ef1f8ad886d0d",
              "status": "affected",
              "version": "2f487712b89376fce267223bbb0db93d393d4b09",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/tipc/group.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.15"
            },
            {
              "lessThan": "4.15",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.271",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.222",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.189",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.158",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.112",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.55",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.9",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.271",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.15.222",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.1.189",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.158",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.112",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.55",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.9",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "4.15",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\ntipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow\n\nCommit 48a5fe38772b (\"tipc: fix bc_ackers underflow on duplicate\nGRP_ACK_MSG\") rejected duplicate/stale ACKs in tipc_group_proto_rcv()\nby returning early when less_eq(acked, m-\u003ebc_acked).\n\nHowever, that check remains incomplete in two ways:\n\n1. When grp-\u003ebc_ackers is zero (e.g. on a quiet group, when replicast\n   ACKs were not requested, or after all expected members have already\n   acknowledged), an unexpected GRP_ACK_MSG with acked \u003e m-\u003ebc_acked\n   passes less_eq() and unconditionally decrements grp-\u003ebc_ackers.\n   Because bc_ackers is a u16, this wraps to 65535, causing\n   tipc_group_bc_cong() to permanently report congestion and blocking\n   all future group broadcasts on the socket.\n\n2. During an active broadcast round (grp-\u003ebc_ackers \u003e 0), the sender\n   transmits packet S and advances grp-\u003ebc_snd_nxt to S + 1. Receivers\n   increment their expected counter to S + 1 upon consuming packet S,\n   so the only valid ACK value for the current round is strictly\n   acked == grp-\u003ebc_snd_nxt.\n\n   However, tipc_group_update_bc_members() initializes each member\u0027s\n   m-\u003ebc_acked to prev = grp-\u003ebc_snd_nxt - 1 (S - 1 before increment).\n   This leaves a 2-sequence gap (S - 1 to S + 1) in sequence space.\n   An incoming ACK is therefore neither rejected as duplicate nor\n   prevented from decrementing grp-\u003ebc_ackers if an unexpected or stale\n   value (such as S) is received. A member sending acked = S followed\n   by acked = S + 1 could decrement grp-\u003ebc_ackers twice in the same\n   round, prematurely clearing bc_ackers or underflowing it.\n\nFix this by:\n- Dropping GRP_ACK_MSG immediately if grp-\u003ebc_ackers is zero.\n- Requiring acked == grp-\u003ebc_snd_nxt and rejecting duplicates where\n  m-\u003ebc_acked == acked. Because replicast broadcast rounds are strictly\n  sequential, only grp-\u003ebc_snd_nxt can be acknowledged, and each member\n  can acknowledge at most once per round.\n\nNote that a related pre-existing issue in tipc_group_delete_member()\n(where grp-\u003ebc_ackers decrementing to zero upon member departure does\nnot restore *grp-\u003eopen or trigger a socket wakeup) will be addressed\nin a separate patch."
        }
      ],
      "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 - A crafted UDP/IP TIPC GROUP_PROTOCOL/GRP_ACK_MSG carrying attacker-controlled msg_grp_bc_acked() reaches tipc_group_proto_rcv() through tipc_udp_recv(), tipc_rcv(), link delivery, and socket filtering. The UDP bearer is routable.\nAC:L - After becoming a recognized group member, the attacker can send one ACK that compares newer than m-\u003ebc_acked while grp-\u003ebc_ackers is zero, deterministically causing the underflow. No race or external condition is required.\nPR:N - The GRP_ACK_MSG case in tipc_group_proto_rcv() verifies only that the packet\u0027s origin node and port match a tipc_member; it performs no credential or capability check. TIPC wire encryption is optional, so no victim-system privilege is required.\nUI:N - Once a cluster-scope TIPC group socket exists, the remote member triggers tipc_group_proto_rcv() solely by sending the crafted GRP_ACK_MSG; no victim action is needed.\nS:U - The malformed ACK changes grp-\u003ebc_ackers and availability of the same kernel-managed TIPC group socket; it does not cross a VM, sandbox, or other security-authority boundary.\nC:N - The faulty operation is a decrement of the u16 grp-\u003ebc_ackers field from zero to 65535. It neither reads outside an object nor returns kernel or application data to the sender.\nI:N - The bug alters only TIPC ACK-accounting state through the intended grp-\u003ebc_ackers field; it provides no out-of-bounds write, control-flow primitive, or modification of application data.\nA:H - After grp-\u003ebc_ackers wraps to 65535, tipc_group_bc_cong() continually reports congestion and tipc_send_group_bcast() blocks or fails all later broadcasts on that socket until the group is recreated."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-24T14:09:23.470Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/edc6593c442278fceff0120e8cc58bc592168c35"
        },
        {
          "url": "https://git.kernel.org/stable/c/9b94a90651e1fa573c6ac6a5a6b269d5874df2c0"
        },
        {
          "url": "https://git.kernel.org/stable/c/507a27435b2bb1f22e3a3674f6a6553eb815021b"
        },
        {
          "url": "https://git.kernel.org/stable/c/80a9ccfc24d3776ef6753a57315e726475fac7d7"
        },
        {
          "url": "https://git.kernel.org/stable/c/478fb08d0c2a53002a721d22b8d6681ec971d90f"
        },
        {
          "url": "https://git.kernel.org/stable/c/12cc3a1eac5a2a06b67a7b85f0f48ff241a94d1b"
        },
        {
          "url": "https://git.kernel.org/stable/c/b0e517961f09b9f60d338d1ea4e17aacdbf206f0"
        },
        {
          "url": "https://git.kernel.org/stable/c/99cc2a62e07a44a22254d7beca9ef1f8ad886d0d"
        }
      ],
      "title": "tipc: reject invalid and unexpected GRP_ACK_MSG to prevent bc_ackers underflow",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98550",
    "datePublished": "2026-10-18T15:18:18.173Z",
    "dateReserved": "2026-09-25T10:25:14.356Z",
    "dateUpdated": "2026-10-24T14:09:23.470Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.