# CVE-2026-74659: net: bridge: mrp: fix uninitialised bytes on the wire

> An attacker on the local network segment can read uninitialized kernel memory from MRP test frames if the bridge MRP feature is enabled.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 22 Aug 2026
- **Also known as:** BELL-CVE-2026-74659, DEBIAN-CVE-2026-74659, GHSA-j5v6-9qh5-x594, UBUNTU-CVE-2026-74659

## What is CVE-2026-74659?

CVE-2026-74659 is a vulnerability in Linux, published on 22 Aug 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:

net: bridge: mrp: fix uninitialised bytes on the wire

br_mrp_alloc_test_skb() builds MRP test frames on an skb from
dev_alloc_skb(), which does not clear the linear data area.  On the MRA
ring-role branch the sub-option TLV header is appended with

	sub_tlv = skb_put(skb, sizeof(*sub_tlv));
	sub_tlv->type = BR_MRP_SUB_TLV_HEADER_TEST_AUTO_MGR;

so sub_tlv->length is never written, and the two trailing alignment bytes
are appended with a bare skb_put() that does not clear them either.  The
neighbouring oui and sub_opt regions are explicitly zeroed, so three
uninitialised bytes are left in every MRA MRP_Test frame that goes out.

Put the sub-option TLV header and the alignment padding in a single
skb_put_zero(), which clears both.  The AUTO_MGR sub-TLV carries no
payload, so the zeroed length field is already the value it should have.

## Which versions are affected by CVE-2026-74659?


## How do I fix CVE-2026-74659?

Apply the vendor's patch.

## Is CVE-2026-74659 being exploited?

There is no known exploitation of CVE-2026-74659 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74659 and fix it if it is affected.

What it is: CVE-2026-74659 is a vulnerability in Linux, published on 22 Aug 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-2026-74659 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-2026-74659/ (Markdown: https://insights.sbomify.com/CVE-2026-74659/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74659
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74659
- OSV: https://osv.dev/vulnerability/CVE-2026-74659

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74659/
Summaries are generated and may contain mistakes; the official description above is the record.