# CVE-2025-40221: media: pci: mg4b: fix uninitialized iio scan data

> A local attacker can read uninitialized stack memory from the mg4b PCI media driver, potentially exposing sensitive kernel data.

- **Severity:** Not scored
- **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:** 4 Dec 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-40221, DEBIAN-CVE-2025-40221, GHSA-vg7m-wj99-9pxm, ROOT-OS-UBUNTU-2404-CVE-2025-40221, UBUNTU-CVE-2025-40221

## What is CVE-2025-40221?

CVE-2025-40221 is a vulnerability in Linux, published on 4 Dec 2025. 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:

media: pci: mg4b: fix uninitialized iio scan data

Fix potential leak of uninitialized stack data to userspace by ensuring
that the `scan` structure is zeroed before use.

## Which versions are affected by CVE-2025-40221?


## How do I fix CVE-2025-40221?

Apply the vendor's patch.

## Is CVE-2025-40221 being exploited?

There is no known exploitation of CVE-2025-40221 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40221 and fix it if it is affected.

What it is: CVE-2025-40221 is a vulnerability in Linux, published on 4 Dec 2025. 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-2025-40221 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-2025-40221/ (Markdown: https://insights.sbomify.com/CVE-2025-40221/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40221
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40221
- OSV: https://osv.dev/vulnerability/CVE-2025-40221

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40221/
Summaries are generated and may contain mistakes; the official description above is the record.