# CVE-2025-39939: iommu/s390: Fix memory corruption when using identity domain

> A memory corruption vulnerability in the Linux kernel's s390 IOMMU driver allows attackers to cause denial of service or potentially execute code when using identity domains.

- **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:** 4 Oct 2025
- **Updated:** 15 Oct 2026
- **Also known as:** BELL-CVE-2025-39939, DEBIAN-CVE-2025-39939, GHSA-pm9c-rrjm-4v2f, UBUNTU-CVE-2025-39939

## What is CVE-2025-39939?

CVE-2025-39939 is a high-severity memory corruption vulnerability in Linux kernel, published on 4 Oct 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:

iommu/s390: Fix memory corruption when using identity domain

zpci_get_iommu_ctrs() returns counter information to be reported as part
of device statistics; these counters are stored as part of the s390_domain.
The problem, however, is that the identity domain is not backed by an
s390_domain and so the conversion via to_s390_domain() yields a bad address
that is zero'd initially and read on-demand later via a sysfs read.
These counters aren't necessary for the identity domain; just return NULL
in this case.

This issue was discovered via KASAN with reports that look like:
BUG: KASAN: global-out-of-bounds in zpci_fmb_enable_device
when using the identity domain for a device on s390.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2025-39939?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-39939?

Apply the vendor's patch.

## Is CVE-2025-39939 being exploited?

There is no known exploitation of CVE-2025-39939 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-2025-39939 and fix it if it is affected.

What it is: CVE-2025-39939 is a high-severity memory corruption vulnerability in Linux kernel, published on 4 Oct 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-2025-39939 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-2025-39939/ (Markdown: https://insights.sbomify.com/CVE-2025-39939/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-39939
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-39939
- OSV: https://osv.dev/vulnerability/CVE-2025-39939

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-39939/
Summaries are generated and may contain mistakes; the official description above is the record.