# CVE-2026-99117: net: bridge: mcast: don't truncate the port group walk on teardown


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111215, BELL-CVE-2026-99117, DEBIAN-CVE-2026-99117, GHSA-phhg-87vx-7j2v, UBUNTU-CVE-2026-99117

## What is CVE-2026-99117?

CVE-2026-99117 is a vulnerability in Linux, published on 28 Oct 2026. 

### Official description

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

net: bridge: mcast: don't truncate the port group walk on teardown

__br_multicast_disable_port_ctx() and br_multicast_del_port() walk
port->mglist with hlist_for_each_entry_safe(). However,
br_multicast_find_del_pg() can also delete other entries from the same
list through br_multicast_fwd_src_remove() or __fwd_del_star_excl().

If such an entry is the iterator's saved next node, hlist_del_init()
clears its ->next and terminates the walk early. The reproducer triggers
this in both teardown walks, leaving port groups in the bridge mdb with
a dangling ->key.port after del_nbp() frees the port:

  BUG: KASAN: slab-use-after-free in __mdb_fill_info+0x1191/0x1320
   __mdb_fill_info+0x1191/0x1320
   br_mdb_dump+0x594/0xe40
   rtnl_mdb_dump+0x1cf/0x5d0

Use hlist_del_init_rcu() to unlink the group while preserving ->next.
br_multicast_del_pg() and the teardown walks run under
br->multicast_lock. The GC worker must acquire the same lock before
detaching the group for destruction, so the node remains alive while
the walk uses the preserved pointer.

Preserving ->next means a walk can now reach a group that an earlier
iteration already deleted as a side effect. That group is off mp->ports,
so br_multicast_find_del_pg() would fall through its port scan and hit
the trailing WARN_ON(1). Skip such groups at the top of that helper: a
port group is put on port->mglist when it is created and only unlinked
when it is deleted, so hlist_unhashed() identifies exactly this case.

## Which versions are affected by CVE-2026-99117?


## How do I fix CVE-2026-99117?

Upgrade to a fixed version.

## Is CVE-2026-99117 being exploited?

There is no known exploitation of CVE-2026-99117 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-99117 and fix it if it is affected.

What it is: CVE-2026-99117 is a vulnerability in Linux, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-99117 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-2026-99117/ (Markdown: https://insights.sbomify.com/CVE-2026-99117/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-99117
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-99117
- OSV: https://osv.dev/vulnerability/CVE-2026-99117

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-99117/
Summaries are generated and may contain mistakes; the official description above is the record.