---
id: "CVE-2026-98554"
kind: "vulnerability"
aliases: ["CVE-2026-98554"]
title: "Linux kernel: VLAN transmit path can crash on short headroom"
severity: "unknown"
cvss: null
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["kernel", "linux", "runtime", "self-hosted", "vlan"]
not_affected_if: ["no-vlan-devices"]
published_at: "2026-10-18T16:17:07+00:00"
first_seen_at: "2026-10-23T21:57:15+00:00"
updated_at: "2026-10-25T05:23:29+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98554", "first_seen_at": "2026-10-23T21:57:15+00:00"}]
---

# Linux kernel: VLAN transmit path can crash on short headroom

The Linux kernel's VLAN header builder can run with too little headroom in a packet buffer, which triggers a skb_under_panic kernel crash. The sources do not describe code execution or data exposure.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- `uname -r` and compare against the fixed kernel builds in the distribution's advisory (unknown from the sources)
- `ip -d link show` to see whether VLAN devices are in use (reorder_hdr flag)

## Fix

- Update the Linux kernel to a build that includes the upstream commit 'vlan: ensure sufficient headroom in vlan_dev_hard_header()' (fixed version unknown from the sources)

## Timeline

- 2026-10-23T21:57:15+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-98554

## From the sources

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

vlan: ensure sufficient headroom in vlan_dev_hard_header()

Callers that only reserve ETH_HLEN or less (such as llc_alloc_frame()),
or skbs allocated before dynamic device/headroom changes (e.g. toggling
VLAN_FLAG_REORDER_HDR or bonding/team switching slaves), can reach
vlan_dev_hard_header() with insufficient headroom and trigger
skb_under_panic().

Use skb_cow_head() in vlan_dev_hard_header() when VLAN_FLAG_REORDER_HDR
is not set to ensure sufficient headroom for the VLAN header(s) and the
underlying device hard header.

Use READ_ONCE() to read dev->hard_header_len and dev->needed_headroom as
they can be updated concurrently under RTNL (e.g. in
vlan_transfer_features()) while vlan_dev_hard_header() runs locklessly on
the transmit path. Also avoid LL_RESERVED_SPACE(dev) here so that the
extra HH_DATA_MOD alignment padding does not trigger unnecessary
pskb_expand_head() reallocations on inner stacked VLAN devices after the
outer VLAN header has been pushed.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_