In Zephyr's Bluetooth Mesh PB-ADV provisioning bearer (subsys/bluetooth/mesh/pbadv.c), provmsgrecv() rescheduled the provisioning protocol watchdog timer unconditionally at the top of the function, before the FCS check and before the ADVLINKINVALID check. Once a provisioning attempt fails, provfailed() sets ADVLINKINVALID and the only recovery path is the protocol timer firing (protocoltimeout -> provlinkclose -> closelink -> resetadvlink and re-enabling of scanning and the unprovisioned device beacon).

A remote, unauthenticated attacker on the BLE advertising channel can first induce a provisioning failure (e.g. with a malformed generic-provisioning PDU) and then transmit any FCS-valid PB-ADV transaction PDU on the same link ID more often than once per protocol timeout (60 s, or 120 s for OOB input/output). Because each such packet reset the timer even on an invalidated link, protocoltimeout never fired, the dead link was never torn down, and the device remained pinned in an un-provisionable state with its unprovisioned beacon disabled and new Link Open requests rejected.

PB-ADV PDUs are processed without authentication and the FCS is a keyless CRC, so no pairing or prior trust is required and the attacker chooses the link ID itself. The impact is a persistent denial of provisioning/re-provisioning service; there is no memory-safety, confidentiality, or integrity impact.

The vulnerable code shipped in releases through v4.4.1. The fix moves the timer reschedule to after the ADVLINKINVALID check (and the FCS check before the reset) so an invalidated link can no longer be kept alive by incoming packets.