# CVE-2025-21896: fuse: revert back to __readahead_folio() for readahead

> A use-after-free vulnerability in the Linux kernel's FUSE filesystem allows attackers to potentially execute code or escalate privileges via splice pipe responses.

- **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:** 1 Apr 2025
- **Updated:** 5 Aug 2026
- **Also known as:** BELL-CVE-2025-21896, GHSA-4r9v-r5j3-85m7, UBUNTU-CVE-2025-21896

## What is CVE-2025-21896?

CVE-2025-21896 is a high-severity use after free vulnerability in Linux kernel, published on 1 Apr 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:

fuse: revert back to __readahead_folio() for readahead

In commit 3eab9d7bc2f4 ("fuse: convert readahead to use folios"), the
logic was converted to using the new folio readahead code, which drops
the reference on the folio once it is locked, using an inferred
reference on the folio. Previously we held a reference on the folio for
the entire duration of the readpages call.

This is fine, however for the case for splice pipe responses where we
will remove the old folio and splice in the new folio (see
fuse_try_move_page()), we assume that there is a reference held on the
folio for ap->folios, which is no longer the case.

To fix this, revert back to __readahead_folio() which allows us to hold
the reference on the folio for the duration of readpages until either we
drop the reference ourselves in fuse_readpages_end() or the reference is
dropped after it's replaced in the page cache in the splice case.
This will fix the UAF bug that was reported.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2025-21896?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21896?

Apply the vendor's patch.

## Is CVE-2025-21896 being exploited?

There is no known exploitation of CVE-2025-21896 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-2025-21896 and fix it if it is affected.

What it is: CVE-2025-21896 is a high-severity use after free vulnerability in Linux kernel, published on 1 Apr 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-2025-21896 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-2025-21896/ (Markdown: https://insights.sbomify.com/CVE-2025-21896/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21896
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21896
- OSV: https://osv.dev/vulnerability/CVE-2025-21896

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21896/
Summaries are generated and may contain mistakes; the official description above is the record.