# CVE-2025-39681: x86/cpu/hygon: Add missing resctrl_cpu_detect() in bsp_init helper

> A missing initialization in the Hygon CPU driver causes a division by zero fault during boot, leading to a denial of service on affected Linux systems.

- **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:** 5 Sep 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-67043, AZL-73692, BELL-CVE-2025-39681, DEBIAN-CVE-2025-39681, GHSA-xfjg-jx94-93h4, ROOT-OS-DEBIAN-11-CVE-2025-39681, ROOT-OS-UBUNTU-2204-CVE-2025-39681, ROOT-OS-UBUNTU-2404-CVE-2025-39681, UBUNTU-CVE-2025-39681

## What is CVE-2025-39681?

CVE-2025-39681 is a medium-severity vulnerability in Debian Debian Linux, published on 5 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/cpu/hygon: Add missing resctrl_cpu_detect() in bsp_init helper

Since

  923f3a2b48bd ("x86/resctrl: Query LLC monitoring properties once during boot")

resctrl_cpu_detect() has been moved from common CPU initialization code to
the vendor-specific BSP init helper, while Hygon didn't put that call in their
code.

This triggers a division by zero fault during early booting stage on our
machines with X86_FEATURE_CQM* supported, where get_rdt_mon_resources() tries
to calculate mon_l3_config with uninitialized boot_cpu_data.x86_cache_occ_scale.

Add the missing resctrl_cpu_detect() in the Hygon BSP init helper.

  [ bp: Massage commit message. ]

## Which versions are affected by CVE-2025-39681?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-39681?

Apply the vendor's patch.

## Is CVE-2025-39681 being exploited?

There is no known exploitation of CVE-2025-39681 in the wild and no public exploit code.

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- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-39681 and fix it if it is affected.

What it is: CVE-2025-39681 is a medium-severity vulnerability in Debian Debian Linux, published on 5 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-2025-39681 in the wild and no public exploit code.

Affected product: Debian Debian 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-2025-39681/ (Markdown: https://insights.sbomify.com/CVE-2025-39681/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39681
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39681
- OSV: https://osv.dev/vulnerability/CVE-2025-39681

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39681/
Summaries are generated and may contain mistakes; the official description above is the record.