# CVE-2026-80978

## Summary

- **CVE ID:** CVE-2026-80978
- **Severity:** HIGH
- **CVSS Score:** 7.8 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## 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.

## Affected Products

- Linux — Linux (1a37e412a0225fcba5587f24c0dfc7636efc8b69)
- Linux — Linux (3.11)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.10.270)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

- [CNA](https://git.kernel.org/stable/c/bc4e05ae66c9797a0972ac44326e69c5305e0020)
- [CNA](https://git.kernel.org/stable/c/af0ee8f04bea22cdb331fa3509e17f81b48938ad)
- [CNA](https://git.kernel.org/stable/c/9144f2c53a04465a6878172b523f640313c5559e)
- [CNA](https://git.kernel.org/stable/c/6b222adeb9340306e2ff97127c76117abb9b3df8)
- [CNA](https://git.kernel.org/stable/c/fb889a619723032140f5d983a3a34d25a5a2bed4)
- [CNA](https://git.kernel.org/stable/c/b160422f8103574425e2834130e169d84c94fa1d)
- [CNA](https://git.kernel.org/stable/c/d36e75f5669140b66515ad3a176ca6337bd80a5e)
- [CNA](https://git.kernel.org/stable/c/84783961cb8bdb36b4f41a02ce43aafc6d52b176)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.13%
- **EPSS Percentile:** 2.9

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._