Jay Beavers

**Name of the Vulnerable Software and Affected Versions** Zephyr versions prior to 4.4.0 **Description** The USB CDC-NCM device class contains a flaw where the `cdc ncm send()` function ignores the return value of `usbd ep enqueue()`. If the enqueue operation fails—which occurs when the USB bus is suspended, disconnected, reset, or the endpoint is disabled—the system attempts to take a completion semaphore using `k sem take(&data-sync sem, K FOREVER)`. Since no data was enqueued, the callback required to signal the semaphore never triggers, causing the shared network traffic-class TX thread to deadlock while holding the interface TX lock. This results in a permanent halt of transmissions and a transmit buffer leak, recoverable only via reboot. This issue leads to a persistent loss of the virtual network connection and may stall egress on other network interfaces. **Recommendations** Update to version 4.4.0 or later to ensure the return value of `usbd ep enqueue()` is checked and buffers are freed before the blocking wait.