# CVE-2025-38563: perf/core: Prevent VMA split of buffer mappings

> A race condition in Linux kernel perf subsystem allows reference count leaks via VMA splits, potentially leading to denial of service.

- **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:** 19 Aug 2025
- **Updated:** 11 May 2026
- **Also known as:** AZL-66494, AZL-73800, BELL-CVE-2025-38563, DEBIAN-CVE-2025-38563, GHSA-722p-jvv6-w5fv, ROOT-OS-DEBIAN-11-CVE-2025-38563, ROOT-OS-DEBIAN-12-CVE-2025-38563, ROOT-OS-UBUNTU-2204-CVE-2025-38563, ROOT-OS-UBUNTU-2404-CVE-2025-38563, UBUNTU-CVE-2025-38563

## What is CVE-2025-38563?

CVE-2025-38563 is a high-severity vulnerability in Debian Debian Linux, 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:

perf/core: Prevent VMA split of buffer mappings

The perf mmap code is careful about mmap()'ing the user page with the
ringbuffer and additionally the auxiliary buffer, when the event supports
it. Once the first mapping is established, subsequent mapping have to use
the same offset and the same size in both cases. The reference counting for
the ringbuffer and the auxiliary buffer depends on this being correct.

Though perf does not prevent that a related mapping is split via mmap(2),
munmap(2) or mremap(2). A split of a VMA results in perf_mmap_open() calls,
which take reference counts, but then the subsequent perf_mmap_close()
calls are not longer fulfilling the offset and size checks. This leads to
reference count leaks.

As perf already has the requirement for subsequent mappings to match the
initial mapping, the obvious consequence is that VMA splits, caused by
resizing of a mapping or partial unmapping, have to be prevented.

Implement the vm_operations_struct::may_split() callback and return
unconditionally -EINVAL.

That ensures that the mapping offsets and sizes cannot be changed after the
fact. Remapping to a different fixed address with the same size is still
possible as it takes the references for the new mapping and drops those of
the old mapping.

## Which versions are affected by CVE-2025-38563?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38563?

Apply the vendor's patch.

## Is CVE-2025-38563 being exploited?

There is no known exploitation of CVE-2025-38563 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

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- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [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-2025-38563 and fix it if it is affected.

What it is: CVE-2025-38563 is a high-severity vulnerability in Debian Debian Linux, 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-2025-38563 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-2025-38563/ (Markdown: https://insights.sbomify.com/CVE-2025-38563/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38563
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38563
- OSV: https://osv.dev/vulnerability/CVE-2025-38563

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38563/
Summaries are generated and may contain mistakes; the official description above is the record.