# CVE-2026-98023: vxlan: reject dynamic fdb entries that reference a nexthop id

> A race condition in Linux kernel VXLAN allows list corruption and use-after-free, potentially causing denial of service or code execution.

- **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:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104193, BELL-CVE-2026-98023, DEBIAN-CVE-2026-98023, GHSA-vcqm-xvp9-x4jq, UBUNTU-CVE-2026-98023

## What is CVE-2026-98023?

CVE-2026-98023 is a high-severity vulnerability in Linux, published on 25 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: reject dynamic fdb entries that reference a nexthop id

The commit cited in the Fixes tag allowed VXLAN FDB entries to point to
FDB nexthops so that overlay traffic could be load balanced across
multiple VTEPs. Such entries can only be configured from user space,
cannot be learned and cannot roam. They only make sense with a user space
control plane such as E-VPN where data plane learning is disabled.

Despite that, the VXLAN driver does not currently prevent such entries
from being configured with the "dynamic" flag. The per-nexthop FDB list
is only protected by the per-device hash lock, which is not sufficient
when two VXLAN devices point to the same FDB nexthop and therefore share
the list. Aging runs in softirq context without RTNL, so an entry deleted
by one device can race with an addition or deletion from the other,
leading to list corruption:

  list_del corruption. next->prev should be ffff8881069d9548, but was
  dead000000000122. (next=ffff8881069d9448)
  WARNING: CPU: 0 PID: 90 at lib/list_debug.c:65
  __list_del_entry_valid_or_report+0x1aa/0x210
  ...
   vxlan_fdb_destroy+0x5b8/0xad0
   vxlan_cleanup+0x328/0x450
   call_timer_fn+0x2a/0x1c0
   run_timer_softirq+0x18c/0x210
  BUG: KASAN: slab-use-after-free in vxlan_fdb_destroy

Fix this by rejecting the bogus configuration of dynamic FDB entries that
point to FDB nexthops, both when created and when an existing entry is
updated. As such, the per-nexthop FDB list is only ever mutated under the
RTNL lock. Add test cases to make sure that this does not regress in the
future.

## Which versions are affected by CVE-2026-98023?


## How do I fix CVE-2026-98023?

Apply the vendor's patch.

## Is CVE-2026-98023 being exploited?

There is no known exploitation of CVE-2026-98023 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98023 and fix it if it is affected.

What it is: CVE-2026-98023 is a high-severity vulnerability in Linux, published on 25 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-2026-98023 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-2026-98023/ (Markdown: https://insights.sbomify.com/CVE-2026-98023/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98023
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98023
- OSV: https://osv.dev/vulnerability/CVE-2026-98023

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98023/
Summaries are generated and may contain mistakes; the official description above is the record.