# CVE-2026-31420: bridge: mrp: reject zero test interval to avoid OOM panic

> A local attacker can trigger a kernel panic and memory exhaustion by setting a zero MRP test interval in the Linux kernel bridge module.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 13 Apr 2026
- **Updated:** 14 Sep 2026
- **Also known as:** BELL-CVE-2026-31420, DEBIAN-CVE-2026-31420, GHSA-644j-vc34-vf98, ROOT-OS-DEBIAN-11-CVE-2026-31420, ROOT-OS-DEBIAN-12-CVE-2026-31420, ROOT-OS-DEBIAN-13-CVE-2026-31420, ROOT-OS-UBUNTU-2204-CVE-2026-31420, ROOT-OS-UBUNTU-2404-CVE-2026-31420, UBUNTU-CVE-2026-31420

## What is CVE-2026-31420?

CVE-2026-31420 is a medium-severity denial of service vulnerability in Linux kernel, published on 13 Apr 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:

bridge: mrp: reject zero test interval to avoid OOM panic

br_mrp_start_test() and br_mrp_start_in_test() accept the user-supplied
interval value from netlink without validation. When interval is 0,
usecs_to_jiffies(0) yields 0, causing the delayed work
(br_mrp_test_work_expired / br_mrp_in_test_work_expired) to reschedule
itself with zero delay. This creates a tight loop on system_percpu_wq
that allocates and transmits MRP test frames at maximum rate, exhausting
all system memory and causing a kernel panic via OOM deadlock.

The same zero-interval issue applies to br_mrp_start_in_test_parse()
for interconnect test frames.

Use NLA_POLICY_MIN(NLA_U32, 1) in the nla_policy tables for both
IFLA_BRIDGE_MRP_START_TEST_INTERVAL and
IFLA_BRIDGE_MRP_START_IN_TEST_INTERVAL, so zero is rejected at the
netlink attribute parsing layer before the value ever reaches the
workqueue scheduling code. This is consistent with how other bridge
subsystems (br_fdb, br_mst) enforce range constraints on netlink
attributes.

Weakness: CWE-667 (Improper Locking)

## Which versions are affected by CVE-2026-31420?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-31420?

Apply the vendor's patch.

## Is CVE-2026-31420 being exploited?

There is no known exploitation of CVE-2026-31420 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31420 and fix it if it is affected.

What it is: CVE-2026-31420 is a medium-severity denial of service vulnerability in Linux kernel, published on 13 Apr 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-2026-31420 in the wild and no public exploit code.

Affected product: Linux kernel. 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-2026-31420/ (Markdown: https://insights.sbomify.com/CVE-2026-31420/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31420
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31420
- OSV: https://osv.dev/vulnerability/CVE-2026-31420

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31420/
Summaries are generated and may contain mistakes; the official description above is the record.