GHSA-V8W5-25MX-Q5R4

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

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

netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation

Ulrich reports a regression with nfqueue:

If an application did not set the 'F_GSO' capability flag and a gso packet with an unconfirmed nf_conn entry is received all packets are now dropped instead of queued, because the check happens after skb_gso_segment(). In that case, we did have exclusive ownership of the skb and its associated conntrack entry. The elevated use count is due to skb_clone happening via skb_gso_segment().

Move the check so that its peformed vs. the aggregated packet.

Then, annotate the individual segments except the first one so we can do a 2nd check at reinject time.

For the normal case, where userspace does in-order reinjects, this avoids packet drops: first reinjected segment continues traversal and confirms entry, remaining segments observe the confirmed entry.

While at it, simplify nf_ct_drop_unconfirmed(): We only care about unconfirmed entries with a refcnt > 1, there is no need to special-case dying entries.

This only happens with UDP. With TCP, the only unconfirmed packet will be the TCP SYN, those aren't aggregated by GRO.

Next patch adds a udpgro test case to cover this scenario.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-45859"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-05-27T14:16:58Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnetfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation\n\nUlrich reports a regression with nfqueue:\n\nIf an application did not set the \u0027F_GSO\u0027 capability flag and a gso\npacket with an unconfirmed nf_conn entry is received all packets are\nnow dropped instead of queued, because the check happens after\nskb_gso_segment().  In that case, we did have exclusive ownership\nof the skb and its associated conntrack entry.  The elevated use\ncount is due to skb_clone happening via skb_gso_segment().\n\nMove the check so that its peformed vs. the aggregated packet.\n\nThen, annotate the individual segments except the first one so we\ncan do a 2nd check at reinject time.\n\nFor the normal case, where userspace does in-order reinjects, this avoids\npacket drops: first reinjected segment continues traversal and confirms\nentry, remaining segments observe the confirmed entry.\n\nWhile at it, simplify nf_ct_drop_unconfirmed(): We only care about\nunconfirmed entries with a refcnt \u003e 1, there is no need to special-case\ndying entries.\n\nThis only happens with UDP.  With TCP, the only unconfirmed packet will\nbe the TCP SYN, those aren\u0027t aggregated by GRO.\n\nNext patch adds a udpgro test case to cover this scenario.",
  "id": "GHSA-v8w5-25mx-q5r4",
  "modified": "2026-05-27T15:33:13Z",
  "published": "2026-05-27T15:33:13Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-45859"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/207b3ebacb6113acaaec0d171d5307032c690004"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/23901aa6b8a2f294c4b774436b4691f3ff863a8f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/79b713ef4261a8ead96af4703f89d0b5f25532e2"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b740e7ddd7ca0dbfeafca3f5e52717206cf28524"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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