# CVE-2026-99041: ip6_gre: remove obsolete ERSPAN PMTU update


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 23 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110918, BELL-CVE-2026-99041, DEBIAN-CVE-2026-99041, GHSA-p22x-mpcm-2h5h, UBUNTU-CVE-2026-99041

## What is CVE-2026-99041?

CVE-2026-99041 is a vulnerability in Linux, published on 23 Oct 2026. 

### Official description

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

ip6_gre: remove obsolete ERSPAN PMTU update

A tc tunnel_key action can attach a METADATA_IP_TUNNEL dst to an skb,
and mirred can redirect it to a native ip6erspan device. The legacy PMTU
update in ip6erspan_tunnel_xmit() treats that metadata dst as a route.
Since it has no output device, dst_dev(dst)->mtu dereferences NULL.

On v7.2 with KASAN, an initial UID/GID 65534 process with CapEff 0 used
self-created user and network namespaces to trigger:

  KASAN: null-ptr-deref
  RIP: ip6erspan_tunnel_xmit+0x10fc/0x2cc0
  Kernel panic - not syncing: Fatal exception in interrupt

The update is obsolete. Commit fe1a4ca0a2b7 ("ip6_gre: process toobig
in a better way") changed IPv6 GRE Too Big handling to update the
underlay route and removed the equivalent block from __gre6_xmit().
ip6_tnl_xmit() then propagates the underlay PMTU to the overlay route.

Remove the stale ERSPAN copy and its now-unused dst variable. This
eliminates the metadata-dst dereference and keeps ERSPAN aligned with
IPv6 GRE PMTU handling.

## Which versions are affected by CVE-2026-99041?


## How do I fix CVE-2026-99041?

Upgrade to a fixed version.

## Is CVE-2026-99041 being exploited?

There is no known exploitation of CVE-2026-99041 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99041 and fix it if it is affected.

What it is: CVE-2026-99041 is a vulnerability in Linux, published on 23 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99041 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-2026-99041/ (Markdown: https://insights.sbomify.com/CVE-2026-99041/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99041
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99041
- OSV: https://osv.dev/vulnerability/CVE-2026-99041

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99041/
Summaries are generated and may contain mistakes; the official description above is the record.