---
id: CVE-2026-10647
title: >-
  The USB CDC-NCM device class (subsys/usb/device_next/class/usbd_cdc_ncm.c)
  ignores the return value of usbd_ep_enqueue() in its ethernet transmit
  callback cdc_ncm_send()
summary: >-
  The USB CDC-NCM device class (subsys/usb/device_next/class/usbd_cdc_ncm.c)
  ignores the return value of usbd_ep_enqueue() in its ethernet transmit
  callback cdc_ncm_send(). When the enqueue fails, the function still calls
  k_sem_take(&data-…
severity: medium
cvss: 5.3
cvssVector: 'CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-833
  - CWE-667
vendor: zephyrproject
product: zephyr
affected:
  - 'zephyr >= 4.1.0, < 4.5.0'
patched:
  - zephyr 4.5.0
published: '2026-06-29'
updated: '2026-08-06'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-10647'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/255bccc1badd1aa06c6e5ddf5b40de8463b33f02
    label: vulnerabilities@zephyrproject.org
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-xcf7-r86m-5q9f
    label: vulnerabilities@zephyrproject.org
tags:
  - nvd
epss: 0.00201
epssPercentile: 0.10263
ingestedAt: '2026-08-07T14:14:17.935Z'
---

## Overview

The USB CDC-NCM device class (subsys/usb/device_next/class/usbd_cdc_ncm.c) ignores the return value of usbd_ep_enqueue() in its ethernet transmit callback cdc_ncm_send(). When the enqueue fails, the function still calls k_sem_take(&data->sync_sem, K_FOREVER), blocking on a completion semaphore that is only ever signaled from the bulk-IN transfer-completion callback. Because nothing was enqueued, that callback never fires and the calling thread — a shared network traffic-class TX thread — deadlocks permanently while holding the interface TX lock, halting transmission until reboot (and leaking the transmit buffer).

The enqueue fails under conditions controlled by the attached USB host: usbd_ep_enqueue() returns -EPERM whenever the bus is suspended (a standard, persistent host operation), and the underlying udc_ep_enqueue() returns -EPERM/-ENODEV on disconnect, bus reset, or endpoint disable. The cdc_ncm_send() guard only checks the DATA_IFACE_ENABLED and IFACE_UP flags, not the suspended state, so a packet transmitted while the host holds the bus suspended reaches the failing enqueue and deadlocks the TX path.

The realistic trigger is a bus suspend that occurs while the exported network interface is active and has traffic to send — host sleep, USB selective/auto-suspend, or hub power management — after which any device-originated packet deadlocks the path, recoverable only by reboot. The impact is a persistent loss of the virtual network connection between the host's NCM interface and the Zephyr device; because the deadlocked thread is a shared traffic-class TX thread, egress on other network interfaces can stall as well. There is no memory corruption or information disclosure.

The defect was introduced with the CDC-NCM driver and shipped in releases through v4.4.0; it is fixed by checking the usbd_ep_enqueue() return value and freeing the buffer before the blocking wait.

## Affected

- `zephyr >= 4.1.0, < 4.5.0`

## Remediation

Upgrade past the affected range:

- `zephyr 4.5.0`