# CVE-2026-63968: ipv6: fix possible infinite loop in fib6_select_path()

> An attacker can trigger an infinite loop in the Linux kernel IPv6 path selection, causing a denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **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 Oct 2026
- **Also known as:** BELL-CVE-2026-63968, DEBIAN-CVE-2026-63968, GHSA-c2hg-pgqh-6wp2, UBUNTU-CVE-2026-63968

## What is CVE-2026-63968?

CVE-2026-63968 is a high-severity 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 fib6_select_path()

Found while auditing the same pattern Sashiko reported in
rt6_fill_node() [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(&first->fib6_siblings)
without waiting for RCU readers; first->fib6_siblings.next then
still points into the old ring and this softirq-side walker never
reaches &first->fib6_siblings as its terminator. fib6_purge_rt()
always WRITE_ONCE()s first->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

Weakness: CWE-835 (Loop with Unreachable Exit Condition)

## Which versions are affected by CVE-2026-63968?


## How do I fix CVE-2026-63968?

Apply the vendor's patch.

## Is CVE-2026-63968 being exploited?

There is no known exploitation of CVE-2026-63968 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-63968 and fix it if it is affected.

What it is: CVE-2026-63968 is a high-severity 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-2026-63968 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-2026-63968/ (Markdown: https://insights.sbomify.com/CVE-2026-63968/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-63968
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-63968
- OSV: https://osv.dev/vulnerability/CVE-2026-63968

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-63968/
Summaries are generated and may contain mistakes; the official description above is the record.