# CVE-2026-19739: Zephyr Bluetooth Link Layer memory leak in connection update

Source: https://junglewise.ai/threats/cve-2026-19739-the-bluetooth-link-layer-control-procedure-code-in-subsys  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-11. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-19739 · Severity: medium · CVSS 6.5 · Published 2026-10-11

The Bluetooth Link Layer controller in Zephyr OS has a memory leak in its connection parameter update procedure. An unauthenticated attacker within radio range can send specially crafted Bluetooth packets to exhaust the controller's fixed pool of receive buffers, causing a denial of service that persists until the device reboots.

Technologies: [Zephyr Project Zephyr OS](https://junglewise.ai/threats/technologies/zephyr-os). Vendors: [Zephyr Project](https://junglewise.ai/threats/vendors/zephyr-project).

## Quick answers

**Is CVE-2026-19739 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-19739 being exploited in the wild.

**How severe is CVE-2026-19739?** Medium severity, with a CVSS score of 6.5, published 11 October 2026.

**Which products and versions are affected?** Zephyr Project Zephyr OS vulnerable versions unspecified in advisory.

**Is there a fix for CVE-2026-19739?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-19739 attacked?** It is attacked from the adjacent network, in an operating system.

**Am I affected by CVE-2026-19739?** Check whether you run Zephyr Project Zephyr OS at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in ull_llcp_conn_upd.c where a retained RX node is not properly released when the connection update procedure receives an invalid PDU while waiting for the update instant. An attacker sends a valid LL_CONNECTION_UPDATE_IND to trigger the procedure, then sends an invalid LL Control PDU (such as LL_LENGTH_REQ) before the instant arrives, causing the procedure to take an error path that fails to release the retained node. Repeating this sequence exhausts the fixed-size RX buffer pool, causing subsequent link-layer receive operations to operate on NULL pointers.

## Affected products

- Zephyr Project Zephyr OS vulnerable versions unspecified in advisory

## Timeline

- 2026-10-11: disclosed

## Related threats

- [Zephyr MCTP over USB use-after-free in packet buffer handling](https://junglewise.ai/threats/cve-2026-85032-the-mctp-over-usb-device-class-in-subsys-pmci-mctp-mctp-usb-c)
- [Zephyr arm64 MMU TLB invalidation memory isolation bypass](https://junglewise.ai/threats/cve-2026-79979-the-arm64-mmu-backend-invalidates-a-single-virtual-address-from)
- [Zephyr UpdateHub firmware client NULL pointer dereference in CoAP probe parsing](https://junglewise.ai/threats/cve-2026-76787-the-updatehub-firmware-over-the-air-client-parses-the-coap-probe)
- [CC1200 sub-GHz IEEE 802.15.4 driver buffer overflow in RX packet parsing](https://junglewise.ai/threats/cve-2026-75084-the-cc1200-sub-ghz-ieee-802-15-4-driver-takes-the-phy-packet)
- [Zephyr Project Bluetooth Link Layer Control Procedure memory leak in CIS creation](https://junglewise.ai/threats/cve-2026-19738-the-bluetooth-link-layer-control-procedure-llcp-implementation)