# CVE-2026-97940: ipv6: fix fib6 walker UAF on seq stop

> A use-after-free in the Linux kernel IPv6 route walker allows attackers to execute arbitrary code or escalate privileges via crafted network operations.

- **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-104700, BELL-CVE-2026-97940, DEBIAN-CVE-2026-97940, GHSA-g66h-hcwj-f29f, UBUNTU-CVE-2026-97940

## What is CVE-2026-97940?

CVE-2026-97940 is a high-severity use after free 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:

ipv6: fix fib6 walker UAF on seq stop

ipv6_route_iter_active() treats a walker in FWS_U at the table root as
already unlinked. fib6_del_route() can move a still-linked walker into
that same state when the current leaf is the last route at the root,
so ipv6_route_native_seq_stop() skips fib6_walker_unlink(). The seq
private object can then be freed while it remains on
net->ipv6.fib6_walkers. A later route deletion walks the dangling list
and uses the freed walker.

Use the list head as membership state and reinitialize it when
unlinking. Keep the existing w->node check so a never-started iterator
with a zeroed private object is not treated as linked.

The same stop helper is used by /proc/net/ipv6_route and by the BPF
ipv6_route iterator. The BPF show path only widens the race.

## Which versions are affected by CVE-2026-97940?


## How do I fix CVE-2026-97940?

Apply the vendor's patch.

## Is CVE-2026-97940 being exploited?

There is no known exploitation of CVE-2026-97940 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97940 and fix it if it is affected.

What it is: CVE-2026-97940 is a high-severity use after free 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-2026-97940 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-2026-97940/ (Markdown: https://insights.sbomify.com/CVE-2026-97940/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97940
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97940
- OSV: https://osv.dev/vulnerability/CVE-2026-97940

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97940/
Summaries are generated and may contain mistakes; the official description above is the record.