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CVE-2026-19739: the future (the node is retained and the procedure enters RP CU STATE WAIT INSTANT), then

Severity

6.5 (MEDIUM)

Vendor

ZEPHYRPROJECT

Patch status

Unknown

Published

2026-10-11T18:16:59.170

Modified

2026-10-11T18:16:59.170

Why it matters

This matters because the affected product may be exploitable without valid credentials. Internet-facing deployments should be reviewed first.

Recommended admin actions

• Review during normal vulnerability triage unless the affected system is internet-facing or business-critical.
• Compare installed versions against the affected version range in the advisory.
• Treat internet-facing systems as higher priority.

Technical 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 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.

View the official NVD record for CVE-2026-19739

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.