# CVE-2026-80838: vxlan: keep the last remote linked during FDB flush

> A race condition in the Linux kernel VXLAN driver allows attackers to trigger a use-after-free, potentially leading to code execution or system crashes.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 4 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-80838, DEBIAN-CVE-2026-80838, GHSA-9cfq-2rjh-r5vr, UBUNTU-CVE-2026-80838

## What is CVE-2026-80838?

CVE-2026-80838 is an use after free vulnerability in Linux, published on 4 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:

vxlan: keep the last remote linked during FDB flush

A non-nexthop FDB entry is expected to have at least one remote while it
remains reachable through the FDB hash table. A filtered bulk flush
violates this invariant when every remote matches: It unlinks the last
remote in vxlan_fdb_dst_destroy() and only afterwards tells vxlan_flush()
to destroy the parent FDB entry.

An RCU reader can find the parent during this interval.
first_remote_rcu() then applies list_entry_rcu() to the empty list head,
producing an invalid remote pointer that the receive learning path can
read from and write to.

When a matching remote is the sole remaining remote, leave it linked and
ask the caller to destroy the entire FDB entry. vxlan_fdb_destroy() keeps
the remote attached while sending the deletion notification and removing
the parent from the lookup structures.

## Which versions are affected by CVE-2026-80838?


## How do I fix CVE-2026-80838?

Apply the vendor's patch.

## Is CVE-2026-80838 being exploited?

There is no known exploitation of CVE-2026-80838 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80838 and fix it if it is affected.

What it is: CVE-2026-80838 is an use after free vulnerability in Linux, published on 4 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-2026-80838 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-2026-80838/ (Markdown: https://insights.sbomify.com/CVE-2026-80838/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80838
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80838
- OSV: https://osv.dev/vulnerability/CVE-2026-80838

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80838/
Summaries are generated and may contain mistakes; the official description above is the record.