# CVE-2025-38084: mm/hugetlb: unshare page tables during VMA split, not before

> A race condition in Linux kernel hugetlb page table unsharing during VMA splits allows attackers to potentially escalate privileges or execute code.

- **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:** 28 Jun 2025
- **Updated:** 15 Oct 2026
- **Also known as:** AZL-64377, BELL-CVE-2025-38084, DEBIAN-CVE-2025-38084, GHSA-mfp4-4cfm-v388, ROOT-OS-DEBIAN-11-CVE-2025-38084, ROOT-OS-DEBIAN-12-CVE-2025-38084, ROOT-OS-UBUNTU-2204-CVE-2025-38084, ROOT-OS-UBUNTU-2404-CVE-2025-38084, UBUNTU-CVE-2025-38084

## What is CVE-2025-38084?

CVE-2025-38084 is a high-severity vulnerability in Debian Debian Linux, published on 28 Jun 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:

mm/hugetlb: unshare page tables during VMA split, not before

Currently, __split_vma() triggers hugetlb page table unsharing through
vm_ops->may_split().  This happens before the VMA lock and rmap locks are
taken - which is too early, it allows racing VMA-locked page faults in our
process and racing rmap walks from other processes to cause page tables to
be shared again before we actually perform the split.

Fix it by explicitly calling into the hugetlb unshare logic from
__split_vma() in the same place where THP splitting also happens.  At that
point, both the VMA and the rmap(s) are write-locked.

An annoying detail is that we can now call into the helper
hugetlb_unshare_pmds() from two different locking contexts:

1. from hugetlb_split(), holding:
    - mmap lock (exclusively)
    - VMA lock
    - file rmap lock (exclusively)
2. hugetlb_unshare_all_pmds(), which I think is designed to be able to
   call us with only the mmap lock held (in shared mode), but currently
   only runs while holding mmap lock (exclusively) and VMA lock

Backporting note:
This commit fixes a racy protection that was introduced in commit
b30c14cd6102 ("hugetlb: unshare some PMDs when splitting VMAs"); that
commit claimed to fix an issue introduced in 5.13, but it should actually
also go all the way back.

[jannh@google.com: v2]

## Which versions are affected by CVE-2025-38084?

It affects 2 products.


Products: Debian Debian Linux, Linux kernel.

## How do I fix CVE-2025-38084?

Apply the vendor's patch.

## Is CVE-2025-38084 being exploited?

There is no known exploitation of CVE-2025-38084 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
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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-2025-38084 and fix it if it is affected.

What it is: CVE-2025-38084 is a high-severity vulnerability in Debian Debian Linux, published on 28 Jun 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-2025-38084 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-2025-38084/ (Markdown: https://insights.sbomify.com/CVE-2025-38084/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-38084
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-38084
- OSV: https://osv.dev/vulnerability/CVE-2025-38084

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-38084/
Summaries are generated and may contain mistakes; the official description above is the record.