# CVE-2026-98278: net: remove WARN_ON_ONCE() from the dev_fill_forward_path() loop check

> A local high-privilege user can trigger a kernel warning and potential denial of service by configuring specific network tunnel routing loops.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** DEBIAN-CVE-2026-98278, GHSA-6vfc-qfc9-vf68, UBUNTU-CVE-2026-98278

## What is CVE-2026-98278?

CVE-2026-98278 is a denial of service vulnerability in Linux, published on 6 Oct 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: remove WARN_ON_ONCE() from the dev_fill_forward_path() loop check

ipip_fill_forward_path() and ip6_tnl_fill_forward_path() look up the
route to the tunnel's remote endpoint and set ctx->dev to its device,
which is the tunnel itself when that route resolves back to the tunnel.
dev_fill_forward_path() then makes no progress and trips
WARN_ON_ONCE(last_dev == ctx->dev) as soon as a flowtable tries to
offload a flow through the tunnel. That routing loop is a configuration
any CAP_NET_ADMIN user can set up, and ip_tunnel_xmit() and
ip6_tnl_xmit() already treat it as a tx error, so remove the warning and
just fail the walk, as commit 008e7a7c293b ("net: remove WARN_ON_ONCE
when accessing forward path array") did for the path stack overflow.

## Which versions are affected by CVE-2026-98278?


## How do I fix CVE-2026-98278?

Apply the vendor's patch.

## Is CVE-2026-98278 being exploited?

There is no known exploitation of CVE-2026-98278 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98278 and fix it if it is affected.

What it is: CVE-2026-98278 is a denial of service vulnerability in Linux, published on 6 Oct 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-2026-98278 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-2026-98278/ (Markdown: https://insights.sbomify.com/CVE-2026-98278/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98278
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98278
- OSV: https://osv.dev/vulnerability/CVE-2026-98278

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98278/
Summaries are generated and may contain mistakes; the official description above is the record.