# CVE-2025-21956: drm/amd/display: Assign normalized_pix_clk when color depth = 14

> A missing case in the AMD display driver causes a kernel warning and potential instability when using 14-bit color depth, requiring a patch.

- **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:** 1 Apr 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-21956, DEBIAN-CVE-2025-21956, GHSA-mq3v-g8q8-f78r, ROOT-OS-UBUNTU-2404-CVE-2025-21956, UBUNTU-CVE-2025-21956

## What is CVE-2025-21956?

CVE-2025-21956 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 Apr 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:

drm/amd/display: Assign normalized_pix_clk when color depth = 14

[WHY & HOW]
A warning message "WARNING: CPU: 4 PID: 459 at ... /dc_resource.c:3397
calculate_phy_pix_clks+0xef/0x100 [amdgpu]" occurs because the
display_color_depth == COLOR_DEPTH_141414 is not handled. This is
observed in Radeon RX 6600 XT.

It is fixed by assigning pix_clk * (14 * 3) / 24 - same as the rests.

Also fixes the indentation in get_norm_pix_clk.

(cherry picked from commit 274a87eb389f58eddcbc5659ab0b180b37e92775)

## Which versions are affected by CVE-2025-21956?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21956?

Apply the vendor's patch.

## Is CVE-2025-21956 being exploited?

There is no known exploitation of CVE-2025-21956 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-2025-21956 and fix it if it is affected.

What it is: CVE-2025-21956 is a medium-severity denial of service vulnerability in Linux kernel, published on 1 Apr 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-2025-21956 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-2025-21956/ (Markdown: https://insights.sbomify.com/CVE-2025-21956/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21956
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21956
- OSV: https://osv.dev/vulnerability/CVE-2025-21956

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21956/
Summaries are generated and may contain mistakes; the official description above is the record.