# CVE-2026-63969: ipv6: fix possible infinite loop in rt6_fill_node()

> An attacker can cause a CPU stall and denial of service in the Linux kernel IPv6 routing code via an infinite loop triggered by concurrent route deletions.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jul 2026
- **Updated:** 19 Jul 2026
- **Also known as:** BELL-CVE-2026-63969, DEBIAN-CVE-2026-63969, GHSA-wc3h-5qqj-xwhm, UBUNTU-CVE-2026-63969

## What is CVE-2026-63969?

CVE-2026-63969 is a denial of service vulnerability in Linux, published on 19 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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

ipv6: fix possible infinite loop in rt6_fill_node()

Sashiko reported this issue [1]. Apply the same fix as
commit f8d8ce1b515a ("ipv6: fix possible infinite loop in fib6_info_uses_dev()").

Writers holding tb6_lock can list_del_rcu(&rt->fib6_siblings)
without waiting for RCU readers; rt->fib6_siblings.next then still
points into the old ring and this softirq-side walker never reaches
&rt->fib6_siblings, causing a CPU stall. fib6_del_route() always
WRITE_ONCE()s rt->fib6_nsiblings to 0 before list_del_rcu(), so an
inside-loop check is a reliable detach signal.

[1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev

## Which versions are affected by CVE-2026-63969?


## How do I fix CVE-2026-63969?

Apply the vendor's patch.

## Is CVE-2026-63969 being exploited?

There is no known exploitation of CVE-2026-63969 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63969 and fix it if it is affected.

What it is: CVE-2026-63969 is a denial of service vulnerability in Linux, published on 19 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-63969 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-2026-63969/ (Markdown: https://insights.sbomify.com/CVE-2026-63969/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63969
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63969
- OSV: https://osv.dev/vulnerability/CVE-2026-63969

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63969/
Summaries are generated and may contain mistakes; the official description above is the record.