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net: bridge: use a stable FDB dst snapshot in RCU readers

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: net: bridge: use a stable FDB dst snapshot in RCU readers Local FDB entries can be rewritten in place by `fdb_delete_local()`, which updates `f->dst` to another port or to `NULL` while keeping the entry alive. Several bridge RCU readers inspect `f->dst`, including `br_fdb_fillbuf()` through the `brforward_read()` sysfs path. These readers currently load `f->dst` multiple times and can therefore observe inconsistent values across the check and later dereference. In `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change `f->dst` after the NULL check and before the `port_no` dereference, leading to a NULL-ptr-deref. Fix this by taking a single `READ_ONCE()` snapshot of `f->dst` in each affected RCU reader and using that snapshot for the rest of the access sequence. Also publish the in-place `f->dst` updates in `fdb_delete_local()` with `WRITE_ONCE()` so the readers and writer use matching access patterns.

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.259, 5.15.210, 6.1.176, 6.12.86, 6.18.27, 6.6.140, 7.0.4
CVEs
CVE-2026-46086
Confirmed fixed CVEs
Not specified
Updated in this feed
2 Nov 2026, 17:04 UTC · Revision 1

Source evidence

net: bridge: use a stable FDB dst snapshot in RCU readers

core-osv · Original source

Published 27 May 2026, 12:58 UTC

In the Linux kernel, the following vulnerability has been resolved: net: bridge: use a stable FDB dst snapshot in RCU readers Local FDB entries can be rewritten in place by `fdb_delete_local()`, which updates `f->dst` to another port or to `NULL` while keeping the entry alive. Several bridge RCU readers inspect `f->dst`, including `br_fdb_fillbuf()` through the `brforward_read()` sysfs path. These readers currently load `f->dst` multiple times and can therefore observe inconsistent values across the check and later dereference. In `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change `f->dst` after the NULL check and before the `port_no` dereference, leading to a NULL-ptr-deref. Fix this by taking a single `READ_ONCE()` snapshot of `f->dst` in each affected RCU reader and using that snapshot for the rest of the access sequence. Also publish the in-place `f->dst` updates in `fdb_delete_local()` with `WRITE_ONCE()` so the readers and writer use matching access patterns.

osv:CVE-2026-46086

Kernel

Fixed versions: 5.10.259, 5.15.210, 6.1.176, 6.6.140, 6.12.86, 6.18.27, 7.0.4

Complete source record
{
  "id": "d78250389997caff0f2a3de60b81118138738ef86c5f4e2bdcb9305aa8a675d1",
  "url": "https://osv.dev/vulnerability/CVE-2026-46086",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net: bridge: use a stable FDB dst snapshot in RCU readers",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net: bridge: use a stable FDB dst snapshot in RCU readers Local FDB entries can be rewritten in place by `fdb_delete_local()`, which updates `f->dst` to another port or to `NULL` while keeping the entry alive. Several bridge RCU readers inspect `f->dst`, including `br_fdb_fillbuf()` through the `brforward_read()` sysfs path. These readers currently load `f->dst` multiple times and can therefore observe inconsistent values across the check and later dereference. In `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change `f->dst` after the NULL check and before the `port_no` dereference, leading to a NULL-ptr-deref. Fix this by taking a single `READ_ONCE()` snapshot of `f->dst` in each affected RCU reader and using that snapshot for the rest of the access sequence. Also publish the in-place `f->dst` updates in `fdb_delete_local()` with `WRITE_ONCE()` so the readers and writer use matching access patterns.",
    "evidence": "osv:CVE-2026-46086",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.259",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.210",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.176",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.140",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.86",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.27",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.0.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-46086",
      "aliases": [
        "CVE-2026-46086"
      ],
      "affected": [
        {
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                {
                  "fixed": "c502fa9f094cb03d1d1685c71e2105ab359bc2b8"
                },
                {
                  "fixed": "a6ae4511c07b91f597e461406c6330f0d4ff810e"
                },
                {
                  "fixed": "1406c4e0ed1eaf8a29801ab1163d00fb7ee4359a"
                },
                {
                  "fixed": "0b9e4bbfb7c949151e3acd44ed4aa33614d2e110"
                },
                {
                  "fixed": "81af4137a30c4c2dc694dea8cacb180bd66000ef"
                },
                {
                  "fixed": "5424e678f9b304e148cf5dcc047cffc7a56a3bb5"
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                {
                  "fixed": "9a2d9d4e657b23dc21f24cf139e3aeff0b61341f"
                },
                {
                  "fixed": "df4601653201de21b487c3e7fffd464790cab808"
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              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-46086.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "3.14.0"
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                {
                  "fixed": "5.10.259"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.11.0"
                },
                {
                  "fixed": "5.15.210"
                }
              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "5.16.0"
                },
                {
                  "fixed": "6.1.176"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.2.0"
                },
                {
                  "fixed": "6.6.140"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.7.0"
                },
                {
                  "fixed": "6.12.86"
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              ]
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            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.13.0"
                },
                {
                  "fixed": "6.18.27"
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              ]
            },
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.19.0"
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                {
                  "fixed": "7.0.4"
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              ]
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-46086.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:21.649736781Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-784472.html",
        "https://git.kernel.org/stable/c/0b9e4bbfb7c949151e3acd44ed4aa33614d2e110",
        "https://git.kernel.org/stable/c/1406c4e0ed1eaf8a29801ab1163d00fb7ee4359a",
        "https://git.kernel.org/stable/c/5424e678f9b304e148cf5dcc047cffc7a56a3bb5",
        "https://git.kernel.org/stable/c/81af4137a30c4c2dc694dea8cacb180bd66000ef",
        "https://git.kernel.org/stable/c/9a2d9d4e657b23dc21f24cf139e3aeff0b61341f",
        "https://git.kernel.org/stable/c/a6ae4511c07b91f597e461406c6330f0d4ff810e",
        "https://git.kernel.org/stable/c/c502fa9f094cb03d1d1685c71e2105ab359bc2b8",
        "https://git.kernel.org/stable/c/df4601653201de21b487c3e7fffd464790cab808",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46086.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-46086",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46086.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-46086",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 487462,
  "published_at": "2026-05-27T12:58:28.137+00:00"
}