CVE-2026-98487 (GCVE-0-2026-98487)
Vulnerability from cvelistv5
Published
2026-10-18 15:16
Modified
2026-10-24 14:09
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net: bridge: mdb: restart port group walk after deletion br_mdb_flush_pgs() keeps a pointer-to-pointer cursor while walking mp->ports. br_multicast_del_pg() can re-enter the same MDB entry through br_multicast_sg_del_exclude_ports() and unlink other port groups. If the cursor points into one of those groups, the next iteration dereferences a stale cursor and can leave mp->ports pointing at freed memory. A following RTM_GETMDB exposes the dangling pointer: BUG: KASAN: slab-use-after-free in br_mdb_dump Read of size 8 br_mdb_dump rtnl_mdb_dump rtnl_dumpit netlink_dump Reset the cursor to mp->ports after every deletion. The deletion removes at least the selected group, so the restarted walk always makes progress.
References
Impacted products
Vendor Product Version
Linux Linux Version: a6acb535afb2a3b688a7858f05b61f0433e480d5
Version: a6acb535afb2a3b688a7858f05b61f0433e480d5
Version: a6acb535afb2a3b688a7858f05b61f0433e480d5
Version: a6acb535afb2a3b688a7858f05b61f0433e480d5
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/bridge/br_mdb.c"
          ],
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        {
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          "product": "Linux",
          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "6.8"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.12.*",
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              "version": "6.12.112",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.55",
              "versionType": "semver"
            },
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              "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": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.112",
                  "versionStartIncluding": "6.8",
                  "vulnerable": true
                },
                {
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                  "versionEndExcluding": "6.18.55",
                  "versionStartIncluding": "6.8",
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                  "vulnerable": true
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                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "6.8",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: mdb: restart port group walk after deletion\n\nbr_mdb_flush_pgs() keeps a pointer-to-pointer cursor while walking\nmp-\u003eports. br_multicast_del_pg() can re-enter the same MDB entry through\nbr_multicast_sg_del_exclude_ports() and unlink other port groups. If the\ncursor points into one of those groups, the next iteration dereferences a\nstale cursor and can leave mp-\u003eports pointing at freed memory.\n\nA following RTM_GETMDB exposes the dangling pointer:\n\n  BUG: KASAN: slab-use-after-free in br_mdb_dump\n  Read of size 8\n    br_mdb_dump\n    rtnl_mdb_dump\n    rtnl_dumpit\n    netlink_dump\n\nReset the cursor to mp-\u003eports after every deletion. The deletion removes at\nleast the selected group, so the restarted walk always makes progress."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - A local sendmsg() on NETLINK_ROUTE carrying RTM_DELMDB with NLM_F_BULK reaches the patched br_mdb_flush_pgs() through rtnl_mdb_del() and ndo_mdb_del_bulk; received bridge packets do not enter this bulk-delete path.\nAC:L - The attacker can add a *,G EXCLUDE membership and permanent static S,G groups so br_multicast_sg_add_exclude_ports() creates skipped kernel-protocol STAR_EXCL nodes; a proto-static bulk flush then deterministically invalidates pp without a race.\nPR:L - rtnetlink_rcv_msg() requires CAP_NET_ADMIN through netlink_net_capable(), but an unprivileged user can obtain that capability in a user-created network namespace and create the bridge, ports, and MDB state there.\nUI:N - The attacker performs the RTM_NEWMDB setup, NLM_F_BULK RTM_DELMDB trigger, and optional RTM_GETMDB traversal through their own netlink socket; no victim action is required.\nS:U - The dangling mp-\u003eports pointer corrupts and exposes bridge objects within the host kernel\u0027s existing security authority; it does not cross a guest-host, hypervisor, or IOMMU boundary.\nC:H - The persistent slab UAF lets reclaimed contents control p-\u003enext and p-\u003ekey.port; br_mdb_fill_info() follows these links and returns port, timer, flag, and source-list data through RTM_GETMDB, enabling kernel-memory disclosure.\nI:H - Reusing the dangling node in br_multicast_del_pg() reaches hlist_del_init_rcu() through reclaimed pg-\u003emglist.pprev and updates rhashtable and GC links, providing attacker-influenced kernel writes and potential control-flow hijacking.\nA:H - After br_multicast_destroy_port_group() calls kfree_rcu(), br_mdb_dump() produces the confirmed slab-use-after-free; stale p-\u003ekey.port or p-\u003enext dereferences in dump or br_multicast_flood can oops or panic the kernel."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-24T14:09:03.998Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/46ec55855c972504258c371677ac039ba20e5d12"
        },
        {
          "url": "https://git.kernel.org/stable/c/ab3c4a4c85f2e1e8d04b5c1770dea8412d21c7fe"
        },
        {
          "url": "https://git.kernel.org/stable/c/fe2a42789c12eb7c5d3a42191e2cc735a6c35ead"
        },
        {
          "url": "https://git.kernel.org/stable/c/ab1404ac81154a89fb61ac50ae9a04cd8d4834dc"
        }
      ],
      "title": "net: bridge: mdb: restart port group walk after deletion",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98487",
    "datePublished": "2026-10-18T15:16:04.746Z",
    "dateReserved": "2026-09-25T10:25:14.352Z",
    "dateUpdated": "2026-10-24T14:09:03.998Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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