# CVE-2025-21734: misc: fastrpc: Fix copy buffer page size

> A flaw in the Linux kernel fastrpc driver allows improper page size calculation, potentially leading to memory corruption and code execution.

- **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:** 27 Feb 2025
- **Updated:** 5 Aug 2026
- **Also known as:** AZL-68970, BELL-CVE-2025-21734, DEBIAN-CVE-2025-21734, GHSA-r5rr-wmp2-hj47, ROOT-OS-DEBIAN-11-CVE-2025-21734, ROOT-OS-UBUNTU-2204-CVE-2025-21734, ROOT-OS-UBUNTU-2404-CVE-2025-21734, UBUNTU-CVE-2025-21734

## What is CVE-2025-21734?

CVE-2025-21734 is a high-severity memory corruption vulnerability in Linux kernel, published on 27 Feb 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:

misc: fastrpc: Fix copy buffer page size

For non-registered buffer, fastrpc driver copies the buffer and
pass it to the remote subsystem. There is a problem with current
implementation of page size calculation which is not considering
the offset in the calculation. This might lead to passing of
improper and out-of-bounds page size which could result in
memory issue. Calculate page start and page end using the offset
adjusted address instead of absolute address.

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

## Which versions are affected by CVE-2025-21734?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21734?

Apply the vendor's patch.

## Is CVE-2025-21734 being exploited?

There is no known exploitation of CVE-2025-21734 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-2025-21734 and fix it if it is affected.

What it is: CVE-2025-21734 is a high-severity memory corruption vulnerability in Linux kernel, published on 27 Feb 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-2025-21734 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-2025-21734/ (Markdown: https://insights.sbomify.com/CVE-2025-21734/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21734
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21734
- OSV: https://osv.dev/vulnerability/CVE-2025-21734

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21734/
Summaries are generated and may contain mistakes; the official description above is the record.