---
id: CVE-2026-19739
title: >-
  The Bluetooth Link Layer control procedure code in
  subsys/bluetooth/controller/ll_sw/ull_llcp_conn_upd.c retains the received RX
  node while a Connection Update / Connection Parameter procedure waits for its
  instant, so the node can later…
summary: >-
  The Bluetooth Link Layer control procedure code in
  subsys/bluetooth/controller/ll_sw/ull_llcp_conn_upd.c retains the received RX
  node while a Connection Update / Connection Parameter procedure waits for its
  instant, so the node can later…
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
  - CWE-459
  - CWE-617
  - CWE-772
published: '2026-10-11'
updated: '2026-10-11'
sourceUpdated: '2026-10-11T18:16:59.170'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-19739'
references:
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/commit/7b600129faaba8bb26dd5cb3e8f17ed1cb41ea7f
    label: vulnerabilities@zephyrproject.org
  - url: >-
      https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-84v8-vgp5-4vc9
    label: vulnerabilities@zephyrproject.org
tags:
  - nvd
ingestedAt: '2026-10-12T14:50:34.067Z'
---

## Overview

The Bluetooth Link Layer control procedure code in subsys/bluetooth/controller/ll_sw/ull_llcp_conn_upd.c retains the received RX node while a Connection Update / Connection Parameter procedure waits for its instant, so the node can later carry the host notification (llcp_rx_node_retain(), which marks it NODE_RX_TYPE_RETAIN and thereby suppresses the normal recycling in ull.c). The default: arm of llcp_rp_cu_rx() and llcp_lp_cu_rx() — the "invalid PDU, terminate the connection" path — completed the procedure without releasing that retained node. llcp_rr_check_done() then dequeued and freed the procedure context with ctx->node_ref.rx still pointing at the retained node, dropping the last reference to it.

A peer device in radio range can reach this without pairing, bonding, or encryption. Against a peripheral, the peer sends a well-formed LL_CONNECTION_UPDATE_IND with an instant a few connection events in the future (the node is retained and the procedure enters RP_CU_STATE_WAIT_INSTANT), then, before the instant is reached, sends any other LL Control PDU such as LL_LENGTH_REQ. ull_cp_rx() routes that PDU into the active remote Connection Update procedure, which takes the invalid-PDU path. The central role is reachable symmetrically after accepting an LL_CONNECTION_PARAM_REQ, and the local-procedure variant is reachable with LL_REJECT_IND.

With CONFIG_BT_CTLR_ASSERT_DEBUG enabled (its default), the resulting state violates the invariant asserted in llcp_rr_check_done(), so the two-PDU sequence produces an immediate fatal error in the controller. With those asserts disabled, each occurrence permanently loses one node from the controller's small fixed RX pool (sized from CONFIG_BT_CTLR_RX_BUFFERS, which defaults to 1); repeating the sequence across reconnections exhausts the pool, after which the link-layer receive path operates on a NULL node. The impact is an unauthenticated, remotely triggerable denial of service persisting until reboot; there is no memory-disclosure or memory-corruption consequence, since the leaked node simply becomes unreachable.

## Remediation

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