---
id: CVE-2026-19738
title: >-
  The Bluetooth Link Layer Control Procedure (LLCP) implementation for Connected
  Isochronous Stream (CIS) creation retains an RX node (ctx->node_ref.rx, marked
  NODE_RX_TYPE_RETAIN) so it can later be reused as the host notification — on
  th…
summary: >-
  The Bluetooth Link Layer Control Procedure (LLCP) implementation for Connected
  Isochronous Stream (CIS) creation retains an RX node (ctx->node_ref.rx, marked
  NODE_RX_TYPE_RETAIN) so it can later be reused as the host notification — on
  th…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-401
published: '2026-10-11'
updated: '2026-10-11'
sourceUpdated: '2026-10-11T18:16:59.050'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-19738'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/fde17f2c3de0118f3796c2a83958ee4ce4b5efd6
    label: vulnerabilities@zephyrproject.org
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-6mcj-5jw8-ff36
    label: vulnerabilities@zephyrproject.org
tags:
  - nvd
ingestedAt: '2026-10-12T14:50:34.067Z'
---

## Overview

The Bluetooth Link Layer Control Procedure (LLCP) implementation for Connected Isochronous Stream (CIS) creation retains an RX node (ctx->node_ref.rx, marked NODE_RX_TYPE_RETAIN) so it can later be reused as the host notification — on the peripheral while awaiting the Host's reply to an LL_CIS_REQ, and on the central for the whole duration of a locally initiated CIS Create. In subsys/bluetooth/controller/ll_sw/ull_llcp_cc.c, the "invalid PDU received" paths of llcp_rp_cc_rx() and llcp_lp_cc_rx() terminated the connection and completed the procedure without releasing that retained node, breaking the invariant checked in llcp_lr_check_done() and llcp_rr_check_done() and orphaning the node's memory.

A peer device within radio range can reach this with a single extra LL Control PDU on an unauthenticated, unencrypted ACL link. Against a peripheral, the attacker sends a valid LL_CIS_REQ and then, before the Host replies, any unrelated LL Control PDU (for example LL_VERSION_IND), which ull_cp_rx() routes into the active remote procedure. Against a central performing a CIS Create, a malicious peripheral answers with LL_UNKNOWN_RSP for CIS_REQ, which is dispatched into the active local procedure. No pairing, encryption or user interaction is required; the code is compiled in when CONFIG_BT_CTLR_PERIPHERAL_ISO or CONFIG_BT_CTLR_CENTRAL_ISO is enabled.

In default builds (CONFIG_BT_CTLR_ASSERT_DEBUG is default y) the retained-node assertion fires immediately, producing a controller fatal error and, typically, a system reset from one injected PDU. With the development assertions disabled, each attempt permanently loses one node from the controller's small LL notification pool (LL_PDU_RX_CNT, 2 * CONFIG_BT_CTLR_LLCP_CONN) together with its memq_link_t; repeating the connect-attack-reconnect cycle exhausts the pool, after which notification allocation always fails, RX flow control stalls, and the non-disableable LL_ASSERT_ERR() in llcp_lp_cc_flush() faults. The impact is limited to availability — the leaked node is orphaned, never reused or double-freed — and recovery requires a reboot.

## Remediation

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