---
id: CVE-2026-80905
title: 'net: tap: fix wrong transport_header when sending VLAN-tagged frame'
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_head…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 <
    c0376820922d255ae1d103c32345a6ec4c3266f7
  - >-
    Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 <
    f1d297cad5c1eacd9fadfd0346ad97405ffbf97c
  - >-
    Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 <
    5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b
  - >-
    Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 <
    88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3
  - >-
    Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 <
    cbb35cbe8db268fefe34c23df15348cf99025298
  - Linux 3cae5ef1f37a475faf7c40bc6a3c170779f3e0b1
  - Linux >= 4.20.1 < 4.21
  - Linux 5.0
published: '2026-09-04'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T12:47:13.437Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-80905'
references:
  - url: 'https://git.kernel.org/stable/c/c0376820922d255ae1d103c32345a6ec4c3266f7'
  - url: 'https://git.kernel.org/stable/c/f1d297cad5c1eacd9fadfd0346ad97405ffbf97c'
  - url: 'https://git.kernel.org/stable/c/5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b'
  - url: 'https://git.kernel.org/stable/c/88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3'
  - url: 'https://git.kernel.org/stable/c/cbb35cbe8db268fefe34c23df15348cf99025298'
tags:
  - cve.org
epss: 0.00206
epssPercentile: 0.10075
ingestedAt: '2026-10-21T12:48:53.748Z'
---

## Overview

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.

## Affected

- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < c0376820922d255ae1d103c32345a6ec4c3266f7`
- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < f1d297cad5c1eacd9fadfd0346ad97405ffbf97c`
- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < 5ffaa5d7f56ab24a8e23cf131eadfef31a3bbc4b`
- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < 88b79ac89ecc04d7f2613f7e1c0b46f0c4ddb2f3`
- `Linux >= 8c76e77f9069f10505c08e02646c3ee11ad79038 < cbb35cbe8db268fefe34c23df15348cf99025298`
- `Linux 3cae5ef1f37a475faf7c40bc6a3c170779f3e0b1`
- `Linux >= 4.20.1 < 4.21`
- `Linux 5.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.