Live › vulnerability › CVE-2026-81039
Go to dashboardThe Zephyr Bluetooth host mis-attributes an incoming connection to the wrong pre-allocated advertising reservation when two extended advertising sets share an identity. A nearby attacker can repeat this until the connection pool is exhausted, so the device stops accepting Bluetooth connections.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-26 17:31 UTC. All times on this page are UTC.
Only devices running Zephyr's Bluetooth host with more than one extended advertising set enabled on the same identity, where one set is undirected and another is directed at a bonded peer. Single-advertising-set configurations are not affected, according to the description. Products that use only one advertising set or no extended advertising can skip it.
No product ranges from the sources yet.
CONFIG_BT_EXT_ADV_MAX_ADV_SET is greater than 1 and whether the application runs an undirected and a directed connectable extended advertising set on the same identity.CONFIG_BT_EXT_ADV_MAX_ADV_SET=1) or avoid running a directed set alongside an undirected one.Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
The Bluetooth host pre-allocates a bt_conn object (a "reservation") from the fixed acl_conns[] pool for every connectable advertising set it starts, in le_adv_start_add_conn() in subsys/bluetooth/host/adv.c. When an incoming peripheral connection completes, find_pending_connect() in subsys/bluetooth/host/hci_core.c looked that reservation up using only the identity and the peer address, with a directed-then-undirected fallback, and had no knowledge of which advertising set actually terminated. With CONFIG_BT_EXT_ADV_MAX_ADV_SET > 1, where the LE Enhanced Connection Complete event is cached until the LE Advertising Set Terminated event identifies the set, this lookup can return the reservation belonging to a different, still-running advertising set.
The defect is reachable over the air by any adjacent device. If an application runs two connectable extended advertising sets on the same identity — one undirected and one directed at a peer P (the common "directed reconnect to a bonded central while still accepting new centrals" pattern) — a remote initiator whose address maps to P connecting on the undirected set causes the directed set's reservation to be consumed instead. The initiator address is chosen freely by the remote device and is not authenticated at link establishment, so no bonding, pairing or prior relationship is required to trigger the mis-attribution.
The undirected set's own reservation is then stranded: its BT_ADV_ENABLED flag has already been cleared, and le_adv_stop_free_conn() — the only path that returns a reservation to the pool — is reached only for sets that are still enabled, so bt_le_ext_adv_stop() returns early and the object is never released. Each occurrence permanently consumes one CONFIG_BT_MAX_CONN slot until bt_disable() or reboot. In application patterns that restart the directed advertising set after each disconnect, an attacker can repeat the sequence until the pool is exhausted, after which connectable advertising fails with -ENOMEM and the device can no longer accept connections. As a side effect the directed set keeps advertising without a reservation, so a genuine connection on it is dropped by bt_hci_disconnect(). The impact is availability only; no memory corruption or information disclosure results, and configurations with a single advertising set are unaffected.
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