# CVE-2026-90111: ip6mr: do not clone dst in ip6mr_cache_report()

> A use-after-free in the Linux kernel IPv6 multicast routing allows attackers to trigger memory corruption and potential code execution via crafted packets.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 17 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-102087, BELL-CVE-2026-90111, DEBIAN-CVE-2026-90111, GHSA-4329-5qmc-m43g, UBUNTU-CVE-2026-90111

## What is CVE-2026-90111?

CVE-2026-90111 is a high-severity use after free vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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

ip6mr: do not clone dst in ip6mr_cache_report()

IPv6 input attaches a non-refcounted (NOREF) dst to skbs under RCU.
When an ingress multicast packet misses MFC lookup,
ip6mr_cache_unresolved() places the skb onto the unresolved queue,
escaping the receive-side RCU grace period.

If the underlying route is deleted and freed, and the MFC queue is later
resolved with a wrong parent interface, ip6_mr_forward() invokes
ip6mr_cache_report(..., MRT6MSG_WRONGMIF), which executes
dst_clone(skb_dst(pkt)) on the freed dst entry, triggering a slab
use-after-free.

Report packets queued to mroute6_sk (a raw socket) and netlink
notifications do not require an attached dst entry.

Fix this by:
1. Removing dst_clone() in ip6mr_cache_report() and ensuring report skbs
   do not hold a dst.
2. Dropping skb_dst before queuing unresolved skbs in
   ip6mr_cache_unresolved(), matching the fact that multicast
   forwarding resolves outgoing routes anew via ip6_route_output().

## Which versions are affected by CVE-2026-90111?


## How do I fix CVE-2026-90111?

Apply the vendor's patch.

## Is CVE-2026-90111 being exploited?

There is no known exploitation of CVE-2026-90111 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-90111 and fix it if it is affected.

What it is: CVE-2026-90111 is a high-severity use after free vulnerability in Linux, published on 17 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-90111 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-2026-90111/ (Markdown: https://insights.sbomify.com/CVE-2026-90111/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-90111
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-90111
- OSV: https://osv.dev/vulnerability/CVE-2026-90111

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-90111/
Summaries are generated and may contain mistakes; the official description above is the record.