# CVE-2025-40270: mm, swap: fix potential UAF issue for VMA readahead

> A race condition in Linux kernel swap VMA readahead can cause a use-after-free, potentially allowing 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:** 6 Dec 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-40270, DEBIAN-CVE-2025-40270, GHSA-hfc9-3847-7v4r, UBUNTU-CVE-2025-40270

## What is CVE-2025-40270?

CVE-2025-40270 is a high-severity use after free vulnerability in Linux, published on 6 Dec 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, swap: fix potential UAF issue for VMA readahead

Since commit 78524b05f1a3 ("mm, swap: avoid redundant swap device
pinning"), the common helper for allocating and preparing a folio in the
swap cache layer no longer tries to get a swap device reference
internally, because all callers of __read_swap_cache_async are already
holding a swap entry reference.  The repeated swap device pinning isn't
needed on the same swap device.

Caller of VMA readahead is also holding a reference to the target entry's
swap device, but VMA readahead walks the page table, so it might encounter
swap entries from other devices, and call __read_swap_cache_async on
another device without holding a reference to it.

So it is possible to cause a UAF when swapoff of device A raced with
swapin on device B, and VMA readahead tries to read swap entries from
device A.  It's not easy to trigger, but in theory, it could cause real
issues.

Make VMA readahead try to get the device reference first if the swap
device is a different one from the target entry.

## Which versions are affected by CVE-2025-40270?


## How do I fix CVE-2025-40270?

Apply the vendor's patch.

## Is CVE-2025-40270 being exploited?

There is no known exploitation of CVE-2025-40270 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40270 and fix it if it is affected.

What it is: CVE-2025-40270 is a high-severity use after free vulnerability in Linux, published on 6 Dec 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-2025-40270 in the wild and no public exploit code.

Affected product: 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-2025-40270/ (Markdown: https://insights.sbomify.com/CVE-2025-40270/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40270
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40270
- OSV: https://osv.dev/vulnerability/CVE-2025-40270

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40270/
Summaries are generated and may contain mistakes; the official description above is the record.