CVE-2026-74480 (GCVE-0-2026-74480)

Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-08-19 16:37
VLAI
Title
net: bridge: stop fast-leave after deleting a port group
Summary
In the Linux kernel, the following vulnerability has been resolved: net: bridge: stop fast-leave after deleting a port group br_multicast_leave_group() iterates mp->ports with pp = &p->next in its fast-leave path. After br_multicast_del_pg() removes p, continuing the loop advances pp through the deleted entry. If multicast-to-unicast was enabled, the bridge can hold multiple port groups for the same port and group with different source MAC addresses. Once multicast-to-unicast is disabled, br_port_group_equal() matches those entries by port only. A fast leave can then delete one entry and continue from its stale next pointer, leaving mp->ports pointing at a deleted port group. Fast leave only needs to remove one matching port group. Break after br_multicast_del_pg() so the loop stops before dereferencing the removed entry.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < d6c32e2e25a9a06ba021030e26b6d602a277eb72 (git)
Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < 482bcb85139addb4e8ac8ed10baeda3e0aad4031 (git)
Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < 1a109cc9890d017c41d77e6c82da739579c49f0b (git)
Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < 159ad90cb929c033308bb39a2c5f8fbf393b77aa (git)
Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < 4695430e8132420bf8de94da3eb36a6cf35fde6b (git)
Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < 0309ebbc570000ea0df11c06b69798e5860c5f6f (git)
Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < 4c57056ca6aace2e9f94ae9298bf49ef6b0c95e4 (git)
Affected: 6db6f0eae6052b70885562e1733896647ec1d807 , < a39789f211b8a4125f0c70e05b30cf715f4f187d (git)
guessed Create a notification for this product.
Linux Linux Affected: 4.11
Unaffected: 0 , < 4.11 (semver)
Unaffected: 5.10.265 , ≤ 5.10.* (semver)
Unaffected: 5.15.216 , ≤ 5.15.* (semver)
Unaffected: 6.1.183 , ≤ 6.1.* (semver)
Unaffected: 6.6.151 , ≤ 6.6.* (semver)
Unaffected: 6.12.103 , ≤ 6.12.* (semver)
Unaffected: 6.18.44 , ≤ 6.18.* (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: stop fast-leave after deleting a port group\n\nbr_multicast_leave_group() iterates mp-\u003eports with pp = \u0026p-\u003enext in\nits fast-leave path. After br_multicast_del_pg() removes p,\ncontinuing the loop advances pp through the deleted entry.\n\nIf multicast-to-unicast was enabled, the bridge can hold multiple port\ngroups for the same port and group with different source MAC\naddresses. Once multicast-to-unicast is disabled,\nbr_port_group_equal() matches those entries by port only. A fast leave\ncan then delete one entry and continue from its stale next pointer,\nleaving mp-\u003eports pointing at a deleted port group.\n\nFast leave only needs to remove one matching port group. Break after\nbr_multicast_del_pg() so the loop stops before dereferencing the\nremoved entry."
        }
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            "version": "3.1"
          },
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              "value": "AV:N - The bug is reached when the bridge network stack processes attacker-supplied IGMP/MLD Leave packets received on a bridge port (br_handle_frame_finish -\u003e br_multicast_rcv -\u003e br_ip4/ip6_multicast_leave_group -\u003e br_multicast_leave_group), requiring no local syscall access.\nAC:L - Once a bridge has IGMP snooping, fast-leave, and leftover duplicate port groups (common on WiFi APs that used multicast-to-unicast), an attacker can reliably trigger the bug by sending IGMP/MLD joins then a Leave; no uncontrollable race or rare timing is required.\nPR:N - No privileges or authentication are required on the target; any host on an attached bridge port can inject IGMP/MLD Leave packets that are processed and reach the vulnerable fast-leave deletion loop.\nUI:N - Exploitation requires only attacker-sent multicast control packets; no victim user action such as opening files, clicking links, or mounting filesystems is needed.\nS:U - Impact is kernel heap corruption and use-after-free within the bridge/multicast subsystem on the same host; it does not cross a VM/hypervisor or IOMMU security boundary by itself.\nC:H - Deleting a port group then continuing the list walk dereferences freed net_bridge_port_group memory and can leave mp-\u003eports dangling, giving a use-after-free read primitive exploitable for arbitrary kernel memory disclosure.\nI:H - Corrupting the mp-\u003eports linked list via stale next pointers after br_multicast_del_pg() enables attacker-influenced kernel heap corruption that can be developed into arbitrary write and privilege escalation.\nA:H - The use-after-free and corrupted multicast database pointers cause kernel oops/panics when subsequent bridge multicast forwarding or MDB operations traverse the broken port-group list, enabling repeatable denial of service."
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        "shortName": "Linux"
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    "dateUpdated": "2026-08-19T16:37:33.031Z",
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A fast leave\\ncan then delete one entry and continue from its stale next pointer,\\nleaving mp-\u003eports pointing at a deleted port group.\\n\\nFast leave only needs to remove one matching port group. 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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-02T14:41:43+00:00",
      "cve": "CVE-2026-74480",
      "id": "CVE-2026-74480",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:fixed": "1218",
      "product_status:known_affected": "260",
      "product_status:known_not_affected": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net: bridge: stop fast-leave after deleting a port group",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74480.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-08-22T00:53:12Z",
      "cve": "CVE-2026-74480",
      "id": "CVE-2026-74480",
      "initial_release_date": "2026-08-15T23:52:05Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74480",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74480.json",
      "version": "4"
    }
  }
}



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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.