GHSA-5V9P-3RFC-6RW2

Vulnerability from github – Published: 2026-04-22 15:31 – Updated: 2026-04-27 15:30
VLAI?
Details

In the Linux kernel, the following vulnerability has been resolved:

net: fix fanout UAF in packet_release() via NETDEV_UP race

packet_release() has a race window where NETDEV_UP can re-register a socket into a fanout group's arr[] array. The re-registration is not cleaned up by fanout_release(), leaving a dangling pointer in the fanout array. packet_release() does NOT zero po->num in its bind_lock section. After releasing bind_lock, po->num is still non-zero and po->ifindex still matches the bound device. A concurrent packet_notifier(NETDEV_UP) that already found the socket in sklist can re-register the hook. For fanout sockets, this re-registration calls __fanout_link(sk, po) which adds the socket back into f->arr[] and increments f->num_members, but does NOT increment f->sk_ref.

The fix sets po->num to zero in packet_release while bind_lock is held to prevent NETDEV_UP from linking, preventing the race window.

This bug was found following an additional audit with Claude Code based on CVE-2025-38617.

Severity ?
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-31504"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-416"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-04-22T14:16:49Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: fix fanout UAF in packet_release() via NETDEV_UP race\n\n`packet_release()` has a race window where `NETDEV_UP` can re-register a\nsocket into a fanout group\u0027s `arr[]` array. The re-registration is not\ncleaned up by `fanout_release()`, leaving a dangling pointer in the fanout\narray.\n`packet_release()` does NOT zero `po-\u003enum` in its `bind_lock` section.\nAfter releasing `bind_lock`, `po-\u003enum` is still non-zero and `po-\u003eifindex`\nstill matches the bound device. A concurrent `packet_notifier(NETDEV_UP)`\nthat already found the socket in `sklist` can re-register the hook.\nFor fanout sockets, this re-registration calls `__fanout_link(sk, po)`\nwhich adds the socket back into `f-\u003earr[]` and increments `f-\u003enum_members`,\nbut does NOT increment `f-\u003esk_ref`.\n\nThe fix sets `po-\u003enum` to zero in `packet_release` while `bind_lock` is\nheld to prevent NETDEV_UP from linking, preventing the race window.\n\nThis bug was found following an additional audit with Claude Code based\non CVE-2025-38617.",
  "id": "GHSA-5v9p-3rfc-6rw2",
  "modified": "2026-04-27T15:30:39Z",
  "published": "2026-04-22T15:31:43Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31504"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/1b4c03f8892d955385c202009af7485364731bb9"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/42156f93d123436f2a27c468f18c966b7e5db796"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/42cfd7898eeed290c9fb73f732af1f7d6b0a703e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/654386baef228c2992dbf604c819e4c7c35fc71b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/75fe6db23705a1d55160081f7b37db9665b1880b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ceccbfc6de720ad633519a226715989cfb065af1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/d0c7cdc15fdf8c4f91aca1928e52295d175b6ec6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ee642b1962caa9aa231c01abbd58bc453ae6b66e"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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