# CVE-2026-80978: net: cap advertised IP tunnel headroom

> A Linux kernel vulnerability allows integer overflow in IP tunnel headroom calculations, potentially causing memory corruption or denial of service.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-100806, BELL-CVE-2026-80978, DEBIAN-CVE-2026-80978, GHSA-p2qp-rm9g-w8f3, UBUNTU-CVE-2026-80978

## What is CVE-2026-80978?

CVE-2026-80978 is a high-severity vulnerability in Linux, published on 11 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:

net: cap advertised IP tunnel headroom

IP tunnel devices derive their advertised needed_headroom from lower
output devices. A stack of user-created devices can make the derived
value larger than the 16-bit skb header offsets can represent. Once IP
output reserves it, skb head expansion can wrap those offsets.

The runtime transmit path already caps a growing needed_headroom at 512.
Apply the same cap when tunnel configuration publishes needed_headroom
derived from a lower output device.

Capping the advertised value is safe: IP tunnel transmit still expands
the skb when a packet needs more headroom. A nonsensical stacked
configuration can therefore incur an extra reallocation, but it cannot
publish an unbounded reservation to upper layers.

## Which versions are affected by CVE-2026-80978?


## How do I fix CVE-2026-80978?

Apply the vendor's patch.

## Is CVE-2026-80978 being exploited?

There is no known exploitation of CVE-2026-80978 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80978 and fix it if it is affected.

What it is: CVE-2026-80978 is a high-severity vulnerability in Linux, published on 11 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-2026-80978 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-2026-80978/ (Markdown: https://insights.sbomify.com/CVE-2026-80978/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80978
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80978
- OSV: https://osv.dev/vulnerability/CVE-2026-80978

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80978/
Summaries are generated and may contain mistakes; the official description above is the record.