# CVE-2025-21972: net: mctp: unshare packets when reassembling

> A memory leak in the Linux kernel MCTP reassembly logic can lead to denial of service when packets are cloned.

- **Severity:** High 8.8 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 1 Apr 2025
- **Updated:** 21 Oct 2026
- **Also known as:** BELL-CVE-2025-21972, DEBIAN-CVE-2025-21972, GHSA-w7xc-x24c-mg52, ROOT-OS-DEBIAN-12-CVE-2025-21972, ROOT-OS-UBUNTU-2204-CVE-2025-21972, ROOT-OS-UBUNTU-2404-CVE-2025-21972, UBUNTU-CVE-2025-21972

## What is CVE-2025-21972?

CVE-2025-21972 is a high-severity memory corruption 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:

net: mctp: unshare packets when reassembling

Ensure that the frag_list used for reassembly isn't shared with other
packets. This avoids incorrect reassembly when packets are cloned, and
prevents a memory leak due to circular references between fragments and
their skb_shared_info.

The upcoming MCTP-over-USB driver uses skb_clone which can trigger the
problem - other MCTP drivers don't share SKBs.

A kunit test is added to reproduce the issue.

Weakness: CWE-401 (Missing Release of Memory after Effective Lifetime)

## Which versions are affected by CVE-2025-21972?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2025-21972?

Apply the vendor's patch.

## Is CVE-2025-21972 being exploited?

There is no known exploitation of CVE-2025-21972 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-2025-21972 and fix it if it is affected.

What it is: CVE-2025-21972 is a high-severity memory corruption 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-2025-21972 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-2025-21972/ (Markdown: https://insights.sbomify.com/CVE-2025-21972/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-21972
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-21972
- OSV: https://osv.dev/vulnerability/CVE-2025-21972

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-21972/
Summaries are generated and may contain mistakes; the official description above is the record.