# CVE-2026-98554: vlan: ensure sufficient headroom in vlan_dev_hard_header()

> A flaw in the Linux kernel VLAN handling can cause a system crash via skb_under_panic when insufficient headroom is reserved, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-108854, BELL-CVE-2026-98554, DEBIAN-CVE-2026-98554, GHSA-xh57-3wrj-366f, UBUNTU-CVE-2026-98554

## What is CVE-2026-98554?

CVE-2026-98554 is a denial of service vulnerability in Linux, published on 18 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

## Which versions are affected by CVE-2026-98554?


## How do I fix CVE-2026-98554?

Apply the vendor's patch.

## Is CVE-2026-98554 being exploited?

There is no known exploitation of CVE-2026-98554 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98554 and fix it if it is affected.

What it is: CVE-2026-98554 is a denial of service vulnerability in Linux, published on 18 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-98554 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-98554/ (Markdown: https://insights.sbomify.com/CVE-2026-98554/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98554
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98554
- OSV: https://osv.dev/vulnerability/CVE-2026-98554

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98554/
Summaries are generated and may contain mistakes; the official description above is the record.