CVE-2026-80905 (GCVE-0-2026-80905)
Vulnerability from cvelistv5
Published
2026-09-04 17:19
Modified
2026-10-30 12:31
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: net: tap: fix wrong transport_header when sending VLAN-tagged frame In tap_get_user_xdp(), when processing a VLAN-tagged frame (e.g. ETH_P_8021Q), skb_set_network_header() is called first to advance network_header past the VLAN tag to the inner protocol header. skb_probe_transport_header() is then called with skb->protocol still set to ETH_P_8021Q, while nhoff (derived from skb_network_offset()) already points past the VLAN tag to the inner protocol header. In __skb_flow_dissect(), proto is initialized to ETH_P_8021Q and nhoff points past the VLAN tag. When the dissector hits case ETH_P_8021Q, it reads a struct vlan_hdr at the current nhoff via __skb_header_pointer(), but that offset contains the inner protocol header (e.g. an IP header). The bytes are misinterpreted as a VLAN header, yielding a garbage encapsulated EtherType that matches no known protocol. The dissector returns false, so skb_probe_transport_header() never calls skb_set_transport_header(), leaving transport_header at its uninitialized sentinel value (~0U). Move skb_set_network_header() to after skb_probe_transport_header(). At the time skb_probe_transport_header() is called, network_header still points to the VLAN header (offset ETH_HLEN), so nhoff is correct and the flow dissector can parse the VLAN header, extract the inner EtherType, and advance nhoff to the inner protocol header, allowing transport_header to be set correctly.
References
Impacted products
Vendor Product Version
Linux Linux Version: 8c76e77f9069f10505c08e02646c3ee11ad79038
Version: 8c76e77f9069f10505c08e02646c3ee11ad79038
Version: 8c76e77f9069f10505c08e02646c3ee11ad79038
Version: 8c76e77f9069f10505c08e02646c3ee11ad79038
Version: 8c76e77f9069f10505c08e02646c3ee11ad79038
Version: 8c76e77f9069f10505c08e02646c3ee11ad79038
Version: 3cae5ef1f37a475faf7c40bc6a3c170779f3e0b1
Version: 4.20.1   ≤
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{
  "containers": {
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          "defaultStatus": "unaffected",
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          "programFiles": [
            "drivers/net/tap.c"
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: tap: fix wrong transport_header when sending VLAN-tagged frame\n\nIn tap_get_user_xdp(), when processing a VLAN-tagged frame (e.g.\nETH_P_8021Q), skb_set_network_header() is called first to advance\nnetwork_header past the VLAN tag to the inner protocol header.\nskb_probe_transport_header() is then called with skb-\u003eprotocol still\nset to ETH_P_8021Q, while nhoff (derived from skb_network_offset())\nalready points past the VLAN tag to the inner protocol header.\n\nIn __skb_flow_dissect(), proto is initialized to ETH_P_8021Q and nhoff\npoints past the VLAN tag. When the dissector hits case ETH_P_8021Q, it\nreads a struct vlan_hdr at the current nhoff via __skb_header_pointer(),\nbut that offset contains the inner protocol header (e.g. an IP header).\nThe bytes are misinterpreted as a VLAN header, yielding a garbage\nencapsulated EtherType that matches no known protocol. The dissector\nreturns false, so skb_probe_transport_header() never calls\nskb_set_transport_header(), leaving transport_header at its uninitialized\nsentinel value (~0U).\n\nMove skb_set_network_header() to after skb_probe_transport_header(). At\nthe time skb_probe_transport_header() is called, network_header still\npoints to the VLAN header (offset ETH_HLEN), so nhoff is correct and the\nflow dissector can parse the VLAN header, extract the inner EtherType,\nand advance nhoff to the inner protocol header, allowing transport_header\nto be set correctly."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-30T12:31:24.447Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/a8f49e83e4447b885376e6a937d62df883cc8824"
        },
        {
          "url": "https://git.kernel.org/stable/c/c0376820922d255ae1d103c32345a6ec4c3266f7"
        },
        {
          "url": "https://git.kernel.org/stable/c/f1d297cad5c1eacd9fadfd0346ad97405ffbf97c"
        },
        {
          "url": "https://git.kernel.org/stable/c/5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b"
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          "url": "https://git.kernel.org/stable/c/88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3"
        },
        {
          "url": "https://git.kernel.org/stable/c/cbb35cbe8db268fefe34c23df15348cf99025298"
        }
      ],
      "title": "net: tap: fix wrong transport_header when sending VLAN-tagged frame",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-80905",
    "datePublished": "2026-09-04T17:19:15.289Z",
    "dateReserved": "2026-08-26T14:34:25.800Z",
    "dateUpdated": "2026-10-30T12:31:24.447Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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