---
id: CVE-2026-79982
title: >-
  Out-of-bounds write in the USB Bluetooth HCI transport class when a
  controller-to-host HCI packet exceeds the bulk endpoint maximum packet size
summary: >-
  The Bluetooth HCI USB transport class of the new USB device stack,
  subsys/usb/device_next/class/bt_hci.c, copies every controller-to-host HCI
  packet into a USB transfer buffer before enqueuing it on an endpoint.
  bt_hci_tx_sync_in() alloc…
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
cwe:
  - CWE-787
vendor: zephyrproject
product: zephyr
affected:
  - zephyr >= 3.3.0 <= 4.4.2
published: '2026-10-23'
updated: '2026-10-23'
sourceUpdated: '2026-10-23T19:56:19.432Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-79982'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/0419defd2391652edc27689d206fcd9c48439d4a
    label: Fix commit
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-w5px-w97v-c3hj
    label: GHSA-w5px-w97v-c3hj
tags:
  - cve.org
ingestedAt: '2026-10-23T20:36:51.535Z'
---

## Overview

The Bluetooth HCI USB transport class of the new USB device stack, subsys/usb/device_next/class/bt_hci.c, copies every controller-to-host HCI packet into a USB transfer buffer before enqueuing it on an endpoint. bt_hci_tx_sync_in() allocated that buffer from bt_hci_ep_pool, a fixed pool whose slots are only USBD_MAX_BULK_MPS bytes (64 on full-speed-only builds), and then performed net_buf_add_mem(buf, bt_buf->data, bt_buf->len) with no length check. HCI event and ACL buffers are sized by CONFIG_BT_BUF_EVT_RX_SIZE and CONFIG_BT_BUF_ACL_RX_SIZE and can be far larger, so the copy runs past the end of the 64-byte slot into the adjacent slots and into whatever follows the statically allocated pool.

The device runs the local Bluetooth controller in raw HCI mode (CONFIG_BT_HCI_RAW), so the oversized packets originate over the air. With the HCI buffer sizes recommended for full-featured controllers, an unauthenticated attacker within Bluetooth range can supply the overflowing bytes: a connected peer that negotiates Data Length Extension can send ACL fragments up to CONFIG_BT_CTLR_DATA_LENGTH_MAX bytes, and an attacker that merely broadcasts extended advertising data reaches the same path through LE Extended Advertising Report events, which the controller fragments only to CONFIG_BT_BUF_EVT_RX_SIZE. In the stock configuration the overflow is already reached without any radio traffic: the mandatory Read Supported Commands command-complete event is 70 bytes and overruns the 64-byte slot by six bytes on every host initialization.

Because net_buf_add_mem() validates tailroom only through an assertion unless CONFIG_NET_BUF_HARDENING is enabled, builds with CONFIG_ASSERT=n — the usual production setting — silently corrupt memory adjacent to the USB buffer pool with attacker-chosen contents, which on a target without memory protection between subsystems can lead to arbitrary code execution. Builds with assertions enabled fail the assertion instead and panic, giving a remotely triggerable denial of service. The fix introduces a separate bt_hci_tx_pool sized to MAX(BT_BUF_ACL_RX_SIZE, BT_BUF_EVT_RX_SIZE) for the controller-to-host direction while leaving the host-to-device pool at the endpoint packet size, which is already bounds-checked during reassembly.

## Affected

- `zephyr >= 3.3.0 <= 4.4.2`

## Remediation

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