# CVE-2026-89562: ip6_gre: fix hardware header length for NBMA tunnels

> Incorrect hardware header length calculation in Linux kernel ip6_gre NBMA tunnels can lead to network instability 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-100340, BELL-CVE-2026-89562, DEBIAN-CVE-2026-89562, GHSA-672h-29w5-4fj2, UBUNTU-CVE-2026-89562

## What is CVE-2026-89562?

CVE-2026-89562 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:

ip6_gre: fix hardware header length for NBMA tunnels

ip6gre_tnl_link_config_route() accumulates the lower device's hardware
header length into dev->hard_header_len whenever header_ops is set. This
is incorrect for both users of header_ops.

ip6gretap and ip6erspan have a fixed Ethernet hardware header length.
For an NBMA ip6gre tunnel, ip6gre_header() creates only the GRE header,
the optional FOU or GUE header, and the outer IPv6 header. The lower
device header is headroom needed later, not part of the tunnel device's
hardware header.

Keep the lower device header in needed_headroom. Set hard_header_len to
the tunnel header length only for ARPHRD_IP6GRE devices with header_ops,
and leave the fixed Ethernet header length unchanged for tap and erspan
devices.

## Which versions are affected by CVE-2026-89562?


## How do I fix CVE-2026-89562?

Apply the vendor's patch.

## Is CVE-2026-89562 being exploited?

There is no known exploitation of CVE-2026-89562 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89562 and fix it if it is affected.

What it is: CVE-2026-89562 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-2026-89562 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-2026-89562/ (Markdown: https://insights.sbomify.com/CVE-2026-89562/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89562
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89562
- OSV: https://osv.dev/vulnerability/CVE-2026-89562

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89562/
Summaries are generated and may contain mistakes; the official description above is the record.