# CVE-2026-98598: ipv6: Prevent rt6_insert_exception() for dying fib6_info.

> A race condition in the Linux kernel IPv6 stack allows attackers to cause a denial of service by stalling network device unregistration through reference leaks.

- **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:** 18 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-108809, BELL-CVE-2026-98598, DEBIAN-CVE-2026-98598, GHSA-3wx3-9xwg-38ff, UBUNTU-CVE-2026-98598

## What is CVE-2026-98598?

CVE-2026-98598 is a denial of service vulnerability in Linux, published on 18 Oct 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: Prevent rt6_insert_exception() for dying fib6_info.

Before the cited commit, fib6_nh_flush_exceptions() always set
from->exception_bucket_flushed = 1 under rt6_exception_lock to
prevent rt6_insert_exception() from inserting a new exception
for a dying fib6_info.

The flag was replaced with the FIB6_EXCEPTION_BUCKET_FLUSHED
bit stored in nh->rt6i_exception_bucket.

The problem is that now the bit is only set when the bucket
is not NULL and fib6_nh_flush_exceptions() is called from
fib6_nh_release() after fib6_ref has already reached zero.

If rt6_insert_exception() is called while the target fib6_info
is being removed via fib6_purge_rt(), a new exception could be
created successfully because rt6_flush_exceptions() no longer
sets the bit.

This creates a reference cycle between the fib6_info and the
exception route, leaking the fib6_info, its nexthop device,
and all per-CPU routes in fib6_nh->rt6i_pcpu, which stalls netdev
unregistration.

[   34.680602] unregister_netdevice: waiting for gre6 to become free. Usage count = 68
[   44.920675] unregister_netdevice: waiting for gre6 to become free. Usage count = 68
[   55.176582] unregister_netdevice: waiting for gre6 to become free. Usage count = 68

Let's call fib6_drop_pcpu_from() before rt6_flush_exceptions(),
to set fib6_destroying before rt6_exception_lock, and check
f6i->fib6_destroying in rt6_insert_exception().

Note that FIB6_EXCEPTION_BUCKET_FLUSHED logic is dead and
we can clean it up in net-next.

## Which versions are affected by CVE-2026-98598?


## How do I fix CVE-2026-98598?

Apply the vendor's patch.

## Is CVE-2026-98598 being exploited?

There is no known exploitation of CVE-2026-98598 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98598 and fix it if it is affected.

What it is: CVE-2026-98598 is a denial of service vulnerability in Linux, published on 18 Oct 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-2026-98598 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-2026-98598/ (Markdown: https://insights.sbomify.com/CVE-2026-98598/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98598
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98598
- OSV: https://osv.dev/vulnerability/CVE-2026-98598

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98598/
Summaries are generated and may contain mistakes; the official description above is the record.