# CVE-2025-38689: x86/fpu: Fix NULL dereference in avx512_status()

> A NULL pointer dereference in the Linux kernel's x86 FPU code can cause a system crash when reading proc files for kernel threads with debug FPU enabled.

- **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:** 4 Sep 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-38689, GHSA-2j25-8cwq-vgvc, ROOT-OS-UBUNTU-2204-CVE-2025-38689, ROOT-OS-UBUNTU-2404-CVE-2025-38689, UBUNTU-CVE-2025-38689

## What is CVE-2025-38689?

CVE-2025-38689 is a medium-severity vulnerability in Linux kernel, published on 4 Sep 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:

x86/fpu: Fix NULL dereference in avx512_status()

Problem
-------
With CONFIG_X86_DEBUG_FPU enabled, reading /proc/[kthread]/arch_status
causes a warning and a NULL pointer dereference.

This is because the AVX-512 timestamp code uses x86_task_fpu() but
doesn't check it for NULL. CONFIG_X86_DEBUG_FPU addles that function
for kernel threads (PF_KTHREAD specifically), making it return NULL.

The point of the warning was to ensure that kernel threads only access
task->fpu after going through kernel_fpu_begin()/_end(). Note: all
kernel tasks exposed in /proc have a valid task->fpu.

Solution
--------
One option is to silence the warning and check for NULL from
x86_task_fpu(). However, that warning is fairly fresh and seems like a
defense against misuse of the FPU state in kernel threads.

Instead, stop outputting AVX-512_elapsed_ms for kernel threads
altogether. The data was garbage anyway because avx512_timestamp is
only updated for user threads, not kernel threads.

If anyone ever wants to track kernel thread AVX-512 use, they can come
back later and do it properly, separate from this bug fix.

[ dhansen: mostly rewrite changelog ]

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2025-38689?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38689?

Apply the vendor's patch.

## Is CVE-2025-38689 being exploited?

There is no known exploitation of CVE-2025-38689 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-2025-38689 and fix it if it is affected.

What it is: CVE-2025-38689 is a medium-severity vulnerability in Linux kernel, published on 4 Sep 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-2025-38689 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-2025-38689/ (Markdown: https://insights.sbomify.com/CVE-2025-38689/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38689
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38689
- OSV: https://osv.dev/vulnerability/CVE-2025-38689

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38689/
Summaries are generated and may contain mistakes; the official description above is the record.