# CVE-2026-97939: ipmr: account multicast table and route memory

> A privileged user in a network namespace can exhaust host memory by creating unaccounted multicast routing tables, causing denial of service.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-104625, BELL-CVE-2026-97939, DEBIAN-CVE-2026-97939, GHSA-9pw8-8xmv-73cr, UBUNTU-CVE-2026-97939

## What is CVE-2026-97939?

CVE-2026-97939 is a denial of service vulnerability in Linux, published on 25 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:

ipmr: account multicast table and route memory

A netadmin in a user+net namespace can create many IPv4 and IPv6
multicast routing tables with MRT_TABLE and MRT6_TABLE. Each unseen
id allocates an mr_table via the shared mr_table_alloc(), links it
into the per-net list, and leaves it until netns teardown. Those
objects were not charged to memcg, so the host unreclaimable slab
grows with the table count.

Account mr_table allocations with GFP_KERNEL_ACCOUNT and mark the
IPv4/IPv6 MFC caches SLAB_ACCOUNT. This matches the established
handling of IP addresses, routes and alternate interface names.

Unresolved MFC entries are still allocated from softIRQ with
GFP_ATOMIC and are not charged. They expire after 10 seconds and are
bounded by the socket receive queue; see commit 0079ad8e8dc3
("ipmr: remove hard code cache_resolve_queue_len limit").

## Which versions are affected by CVE-2026-97939?


## How do I fix CVE-2026-97939?

Apply the vendor's patch.

## Is CVE-2026-97939 being exploited?

There is no known exploitation of CVE-2026-97939 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97939 and fix it if it is affected.

What it is: CVE-2026-97939 is a denial of service vulnerability in Linux, published on 25 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-2026-97939 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-2026-97939/ (Markdown: https://insights.sbomify.com/CVE-2026-97939/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97939
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97939
- OSV: https://osv.dev/vulnerability/CVE-2026-97939

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97939/
Summaries are generated and may contain mistakes; the official description above is the record.