GHSA-QCF5-MJ4W-X99V

Vulnerability from github – Published: 2026-05-27 15:33 – Updated: 2026-09-08 09:35
VLAI
Details

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.

Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-46086"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-476"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-27T14:17:30Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: bridge: use a stable FDB dst snapshot in RCU readers\n\nLocal FDB entries can be rewritten in place by `fdb_delete_local()`, which\nupdates `f-\u003edst` to another port or to `NULL` while keeping the entry\nalive. Several bridge RCU readers inspect `f-\u003edst`, including\n`br_fdb_fillbuf()` through the `brforward_read()` sysfs path.\n\nThese readers currently load `f-\u003edst` multiple times and can therefore\nobserve inconsistent values across the check and later dereference.\nIn `br_fdb_fillbuf()`, this means a concurrent local-FDB update can change\n`f-\u003edst` after the NULL check and before the `port_no` dereference,\nleading to a NULL-ptr-deref.\n\nFix this by taking a single `READ_ONCE()` snapshot of `f-\u003edst` in each\naffected RCU reader and using that snapshot for the rest of the access\nsequence. Also publish the in-place `f-\u003edst` updates in `fdb_delete_local()`\nwith `WRITE_ONCE()` so the readers and writer use matching access patterns.",
  "id": "GHSA-qcf5-mj4w-x99v",
  "modified": "2026-09-08T09:35:30Z",
  "published": "2026-05-27T15:33:23Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-46086"
    },
    {
      "type": "WEB",
      "url": "https://cert-portal.siemens.com/productcert/html/ssa-019113.html"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0b9e4bbfb7c949151e3acd44ed4aa33614d2e110"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1406c4e0ed1eaf8a29801ab1163d00fb7ee4359a"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5424e678f9b304e148cf5dcc047cffc7a56a3bb5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/81af4137a30c4c2dc694dea8cacb180bd66000ef"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/9a2d9d4e657b23dc21f24cf139e3aeff0b61341f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a6ae4511c07b91f597e461406c6330f0d4ff810e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c502fa9f094cb03d1d1685c71e2105ab359bc2b8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/df4601653201de21b487c3e7fffd464790cab808"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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