# CVE-2025-38556: HID: core: Harden s32ton() against conversion to 0 bits

> A malicious HID device with a zero-bit report field can cause a kernel crash via shift-out-of-bounds, leading to denial of service.

- **Severity:** High 7.1 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/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:** 19 Aug 2025
- **Updated:** 11 Jun 2026
- **Also known as:** AZL-66491, AZL-70460, BELL-CVE-2025-38556, DEBIAN-CVE-2025-38556, GHSA-fr7f-qh29-24jq, ROOT-OS-DEBIAN-11-CVE-2025-38556, ROOT-OS-DEBIAN-12-CVE-2025-38556, ROOT-OS-DEBIAN-13-CVE-2025-38556, ROOT-OS-UBUNTU-2204-CVE-2025-38556, ROOT-OS-UBUNTU-2404-CVE-2025-38556, UBUNTU-CVE-2025-38556

## What is CVE-2025-38556?

CVE-2025-38556 is a high-severity denial of service vulnerability in Linux kernel, published on 19 Aug 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:

HID: core: Harden s32ton() against conversion to 0 bits

Testing by the syzbot fuzzer showed that the HID core gets a
shift-out-of-bounds exception when it tries to convert a 32-bit
quantity to a 0-bit quantity.  Ideally this should never occur, but
there are buggy devices and some might have a report field with size
set to zero; we shouldn't reject the report or the device just because
of that.

Instead, harden the s32ton() routine so that it returns a reasonable
result instead of crashing when it is called with the number of bits
set to 0 -- the same as what snto32() does.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2025-38556?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-38556?

Apply the vendor's patch.

## Is CVE-2025-38556 being exploited?

There is no known exploitation of CVE-2025-38556 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-2025-38556 and fix it if it is affected.

What it is: CVE-2025-38556 is a high-severity denial of service vulnerability in Linux kernel, published on 19 Aug 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-2025-38556 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-2025-38556/ (Markdown: https://insights.sbomify.com/CVE-2025-38556/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38556
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38556
- OSV: https://osv.dev/vulnerability/CVE-2025-38556

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38556/
Summaries are generated and may contain mistakes; the official description above is the record.