---
id: CVE-2025-21972
title: 'net: mctp: unshare packets when reassembling'
summary: |-
  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 packe…
severity: high
cvss: 8.8
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 <
    3d0281d0713952e8dd14d6d47e3a9c345c28a3b7
  - >-
    Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 <
    5c47d5bfa7b096cf8890afac32141c578583f8e0
  - >-
    Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 <
    f44fff3d3c6cd67b6f348b821d73c4d6888c7a6e
  - >-
    Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 <
    f5d83cf0eeb90fade4d5c4d17d24b8bee9ceeecc
  - Linux 5.15
published: '2025-04-01'
updated: '2026-10-21'
sourceUpdated: '2026-10-21T12:36:11.201Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-21972'
references:
  - url: 'https://git.kernel.org/stable/c/3d0281d0713952e8dd14d6d47e3a9c345c28a3b7'
  - url: 'https://git.kernel.org/stable/c/5c47d5bfa7b096cf8890afac32141c578583f8e0'
  - url: 'https://git.kernel.org/stable/c/f44fff3d3c6cd67b6f348b821d73c4d6888c7a6e'
  - url: 'https://git.kernel.org/stable/c/f5d83cf0eeb90fade4d5c4d17d24b8bee9ceeecc'
tags:
  - cve.org
epss: 0.00302
epssPercentile: 0.22778
ingestedAt: '2026-10-21T12:48:53.716Z'
---

## Overview

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.

## Affected

- `Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 < 3d0281d0713952e8dd14d6d47e3a9c345c28a3b7`
- `Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 < 5c47d5bfa7b096cf8890afac32141c578583f8e0`
- `Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 < f44fff3d3c6cd67b6f348b821d73c4d6888c7a6e`
- `Linux >= 4a992bbd365094730a31bae1e12a6ca695336d57 < f5d83cf0eeb90fade4d5c4d17d24b8bee9ceeecc`
- `Linux 5.15`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.