# CVE-2026-43484: mmc: core: Avoid bitfield RMW for claim/retune flags

> A race condition in the Linux kernel MMC core allows concurrent updates to corrupt shared bitfields, potentially triggering warnings and causing denial of service.

- **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 May 2026
- **Updated:** 13 May 2026
- **Also known as:** BELL-CVE-2026-43484, DEBIAN-CVE-2026-43484, GHSA-42p4-9577-4wfh, ROOT-OS-DEBIAN-11-CVE-2026-43484, ROOT-OS-UBUNTU-2204-CVE-2026-43484, ROOT-OS-UBUNTU-2404-CVE-2026-43484, UBUNTU-CVE-2026-43484

## What is CVE-2026-43484?

CVE-2026-43484 is a medium-severity vulnerability in Linux kernel, published on 13 May 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:

mmc: core: Avoid bitfield RMW for claim/retune flags

Move claimed and retune control flags out of the bitfield word to
avoid unrelated RMW side effects in asynchronous contexts.

The host->claimed bit shared a word with retune flags. Writes to claimed
in __mmc_claim_host() or retune_now in mmc_mq_queue_rq() can overwrite
other bits when concurrent updates happen in other contexts, triggering
spurious WARN_ON(!host->claimed). Convert claimed, can_retune,
retune_now and retune_paused to bool to remove shared-word coupling.

## Which versions are affected by CVE-2026-43484?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43484?

Apply the vendor's patch.

## Is CVE-2026-43484 being exploited?

There is no known exploitation of CVE-2026-43484 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-2026-43484 and fix it if it is affected.

What it is: CVE-2026-43484 is a medium-severity vulnerability in Linux kernel, published on 13 May 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-2026-43484 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-2026-43484/ (Markdown: https://insights.sbomify.com/CVE-2026-43484/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43484
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43484
- OSV: https://osv.dev/vulnerability/CVE-2026-43484

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43484/
Summaries are generated and may contain mistakes; the official description above is the record.