# CVE-2026-80925: vlan: fix skb_under_panic and races when toggling HW VLAN offload

> A race condition in Linux kernel VLAN handling causes a kernel panic when toggling hardware offload, leading to denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-99948, BELL-CVE-2026-80925, DEBIAN-CVE-2026-80925, GHSA-rp2g-gfw2-xg88, UBUNTU-CVE-2026-80925

## What is CVE-2026-80925?

CVE-2026-80925 is a vulnerability in Linux, published on 9 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

vlan: fix skb_under_panic and races when toggling HW VLAN offload

Toggling hardware VLAN TX offload (NETIF_F_HW_VLAN_CTAG_TX or
NETIF_F_HW_VLAN_STAG_TX) on a lower device invokes vlan_transfer_features(),
which dynamically changed vlandev->hard_header_len.

This causes two issues:
1. Lockless TX paths (e.g. packet_snd in af_packet.c, ip6_finish_output2)
   read dev->hard_header_len without holding RTNL lock. Mutating
   hard_header_len dynamically under RTNL creates a data race where upper
   layers reserve insufficient headroom based on a stale hard_header_len,
   resulting in skb_under_panic when vlan_dev_hard_header() is called.
2. In addition, vlan_transfer_features() updated hard_header_len without
   updating header_ops, causing a mismatch between allocated headroom
   and header creation.

Always setting dev->hard_header_len = real_dev->hard_header_len and
dev->needed_headroom = real_dev->needed_headroom + VLAN_HLEN unconditionally
ensures:
- dev->hard_header_len remains 100% static and immutable at real_dev->hard_header_len,
  eliminating all dynamic runtime updates and data races on hard_header_len.
- Upper layers allocating skbs via LL_RESERVED_SPACE() will always reserve
  sufficient headroom for software VLAN tag insertion (real_dev->hard_header_len +
  real_dev->needed_headroom + VLAN_HLEN).
- vlandev inherits real_dev->needed_tailroom so underlying trailer/padding/ICV
  requirements are honored.
- AF_PACKET SOCK_RAW network header offsets remain correctly aligned at
  real_dev->hard_header_len.
- vlan_header_ops is used unconditionally.

Note to stable teams: Make sure to backport these commits:

e16e960d55a4 ("ipvlan: inherit needed_headroom and needed_tailroom from phy_dev")
cef51860becd ("macvlan: inherit needed_headroom and needed_tailroom from lowerdev")

## Which versions are affected by CVE-2026-80925?


## How do I fix CVE-2026-80925?

Apply the vendor's patch.

## Is CVE-2026-80925 being exploited?

There is no known exploitation of CVE-2026-80925 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80925 and fix it if it is affected.

What it is: CVE-2026-80925 is a vulnerability in Linux, published on 9 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-80925 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-2026-80925/ (Markdown: https://insights.sbomify.com/CVE-2026-80925/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80925
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80925
- OSV: https://osv.dev/vulnerability/CVE-2026-80925

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80925/
Summaries are generated and may contain mistakes; the official description above is the record.