# CVE-2026-98102: ipv6: mcast: fix RCU list diversion in ip6_mc_del1_src()

> A race condition in Linux kernel IPv6 multicast handling allows concurrent readers to miss active sources or examine deleted entries, potentially causing data inconsistency or denial of service.

- **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:** 25 Sep 2026
- **Updated:** 19 Oct 2026
- **Also known as:** AZL-104442, BELL-CVE-2026-98102, DEBIAN-CVE-2026-98102, GHSA-g228-xhf6-wqq6, UBUNTU-CVE-2026-98102

## What is CVE-2026-98102?

CVE-2026-98102 is a vulnerability in Linux, published on 25 Sep 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: mcast: fix RCU list diversion in ip6_mc_del1_src()

When removing a source filter whose count reaches zero, ip6_mc_del1_src()
unlinks psf from pmc->mca_sources. If the filter was previously active,
the code moved psf directly into pmc->mca_tomb by updating psf->sf_next.

Because pmc->mca_sources is traversed locklessly under RCU (e.g. by
ipv6_chk_mcast_addr()), mutating psf->sf_next before a grace period
elapses diverts concurrent readers to the tombstone list. Consequently,
readers miss remaining active sources in pmc->mca_sources and improperly
examine deleted tombstone entries.

Fix this by allocating a new tombstone node for pmc->mca_tomb (as done
in sf_setstate()) and retiring the original psf via kfree_rcu().

## Which versions are affected by CVE-2026-98102?


## How do I fix CVE-2026-98102?

Apply the vendor's patch.

## Is CVE-2026-98102 being exploited?

There is no known exploitation of CVE-2026-98102 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-98102 and fix it if it is affected.

What it is: CVE-2026-98102 is a vulnerability in Linux, published on 25 Sep 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-2026-98102 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-2026-98102/ (Markdown: https://insights.sbomify.com/CVE-2026-98102/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-98102
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-98102
- OSV: https://osv.dev/vulnerability/CVE-2026-98102

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-98102/
Summaries are generated and may contain mistakes; the official description above is the record.