# CVE-2025-21856: s390/ism: add release function for struct device

> A missing release function in the s390 ISM driver allows use-after-free, potentially enabling local attackers to execute code or escalate privileges.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 12 Mar 2025
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2025-21856, DEBIAN-CVE-2025-21856, GHSA-m7rv-xwhq-qx85, UBUNTU-CVE-2025-21856

## What is CVE-2025-21856?

CVE-2025-21856 is a high-severity use after free vulnerability in Linux kernel, published on 12 Mar 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:

s390/ism: add release function for struct device

According to device_release() in /drivers/base/core.c,
a device without a release function is a broken device
and must be fixed.

The current code directly frees the device after calling device_add()
without waiting for other kernel parts to release their references.
Thus, a reference could still be held to a struct device,
e.g., by sysfs, leading to potential use-after-free
issues if a proper release function is not set.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-21856?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21856?

Apply the vendor's patch.

## Is CVE-2025-21856 being exploited?

There is no known exploitation of CVE-2025-21856 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-2025-21856 and fix it if it is affected.

What it is: CVE-2025-21856 is a high-severity use after free vulnerability in Linux kernel, published on 12 Mar 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-2025-21856 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-2025-21856/ (Markdown: https://insights.sbomify.com/CVE-2025-21856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21856
- OSV: https://osv.dev/vulnerability/CVE-2025-21856

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21856/
Summaries are generated and may contain mistakes; the official description above is the record.