---
id: CVE-2025-21704
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  usb: cdc-acm: Check control transfer buffer size before access

  If the first fragment is shorter than struct usb_cdc_notification, we can't
  calculate an expected_size
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  usb: cdc-acm: Check control transfer buffer size before access

  If the first fragment is shorter than struct usb_cdc_notification, we can't
  calculate an expected_size. …
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
cwe:
  - CWE-787
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 2.6.13, < 5.4.291'
  - 'linux_kernel >= 5.5, < 5.10.235'
  - 'linux_kernel >= 5.11, < 5.15.179'
  - 'linux_kernel >= 5.16, < 6.1.129'
  - 'linux_kernel >= 6.2, < 6.6.79'
  - 'linux_kernel >= 6.7, < 6.12.16'
  - 'linux_kernel >= 6.13, < 6.13.4'
  - linux_kernel = 2.6.12
  - linux_kernel = 6.14
patched:
  - linux_kernel 6.13.4
published: '2025-02-22'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:17:28.313'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-21704'
references:
  - url: 'https://git.kernel.org/stable/c/383d516a0ebc8641372b521c8cb717f0f1834831'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6abb510251e75f875797d8983a830e6731fa281c'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7828e9363ac4d23b02419bf2a45b9f1d9fb35646'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/871619c2b78fdfe05afb4e8ba548678687beb812'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/90dd2f1b7342b9a671a5ea4160f408037b92b118'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/a4e1ae5c0533964170197e4fb4f33bc8c1db5cd2'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/e563b01208f4d1f609bcab13333b6c0e24ce6a01'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f64079bef6a8a7823358c3f352ea29a617844636'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://project-zero.issues.chromium.org/issues/395107243'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-265688.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-784472.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00368
epssPercentile: 0.30524
ingestedAt: '2026-10-15T03:30:12.785Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

usb: cdc-acm: Check control transfer buffer size before access

If the first fragment is shorter than struct usb_cdc_notification, we can't
calculate an expected_size. Log an error and discard the notification
instead of reading lengths from memory outside the received data, which can
lead to memory corruption when the expected_size decreases between
fragments, causing `expected_size - acm->nb_index` to wrap.

This issue has been present since the beginning of git history; however,
it only leads to memory corruption since commit ea2583529cd1
("cdc-acm: reassemble fragmented notifications").

A mitigating factor is that acm_ctrl_irq() can only execute after userspace
has opened /dev/ttyACM*; but if ModemManager is running, ModemManager will
do that automatically depending on the USB device's vendor/product IDs and
its other interfaces.

## Affected

- `linux_kernel >= 2.6.13, < 5.4.291`
- `linux_kernel >= 5.5, < 5.10.235`
- `linux_kernel >= 5.11, < 5.15.179`
- `linux_kernel >= 5.16, < 6.1.129`
- `linux_kernel >= 6.2, < 6.6.79`
- `linux_kernel >= 6.7, < 6.12.16`
- `linux_kernel >= 6.13, < 6.13.4`
- `linux_kernel = 2.6.12`
- `linux_kernel = 6.14`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.13.4`