net: cap advertised IP tunnel headroom

{
  "id": "a235a6332a4754d217f696fe70132c0eac3c239a29a849068924813077c3ac96",
  "url": "https://osv.dev/vulnerability/CVE-2026-80978",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net: cap advertised IP tunnel headroom",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net: cap advertised IP tunnel headroom IP tunnel devices derive their advertised needed_headroom from lower output devices. A stack of user-created devices can make the derived value larger than the 16-bit skb header offsets can represent. Once IP output reserves it, skb head expansion can wrap those offsets. The runtime transmit path already caps a growing needed_headroom at 512. Apply the same cap when tunnel configuration publishes needed_headroom derived from a lower output device. Capping the advertised value is safe: IP tunnel transmit still expands the skb when a packet needs more headroom. A nonsensical stacked configuration can therefore incur an extra reallocation, but it cannot publish an unbounded reservation to upper layers.",
    "evidence": "osv:CVE-2026-80978",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.270",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.221",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.188",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.6.157",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.12.109",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.50",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "7.2.4",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-80978",
      "aliases": [
        "CVE-2026-80978"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
      ],
      "affected": [
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          "ranges": [
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              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "introduced": "1a37e412a0225fcba5587f24c0dfc7636efc8b69"
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                {
                  "fixed": "fb889a619723032140f5d983a3a34d25a5a2bed4"
                },
                {
                  "fixed": "b160422f8103574425e2834130e169d84c94fa1d"
                },
                {
                  "fixed": "d36e75f5669140b66515ad3a176ca6337bd80a5e"
                },
                {
                  "fixed": "84783961cb8bdb36b4f41a02ce43aafc6d52b176"
                },
                {
                  "fixed": "bc4e05ae66c9797a0972ac44326e69c5305e0020"
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                {
                  "fixed": "af0ee8f04bea22cdb331fa3509e17f81b48938ad"
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                {
                  "fixed": "9144f2c53a04465a6878172b523f640313c5559e"
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                {
                  "fixed": "6b222adeb9340306e2ff97127c76117abb9b3df8"
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80978.json"
          }
        },
        {
          "ranges": [
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              "type": "ECOSYSTEM",
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                  "introduced": "3.11.0"
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          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-80978.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:23.204135222Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/6b222adeb9340306e2ff97127c76117abb9b3df8",
        "https://git.kernel.org/stable/c/84783961cb8bdb36b4f41a02ce43aafc6d52b176",
        "https://git.kernel.org/stable/c/9144f2c53a04465a6878172b523f640313c5559e",
        "https://git.kernel.org/stable/c/af0ee8f04bea22cdb331fa3509e17f81b48938ad",
        "https://git.kernel.org/stable/c/b160422f8103574425e2834130e169d84c94fa1d",
        "https://git.kernel.org/stable/c/bc4e05ae66c9797a0972ac44326e69c5305e0020",
        "https://git.kernel.org/stable/c/d36e75f5669140b66515ad3a176ca6337bd80a5e",
        "https://git.kernel.org/stable/c/fb889a619723032140f5d983a3a34d25a5a2bed4",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/80xxx/CVE-2026-80978.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-80978",
        "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/2026/80xxx/CVE-2026-80978.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-80978",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 489746,
  "published_at": "2026-09-11T19:42:39.496+00:00"
}