<p>Quantum secure direct communication (QSDC) represents a groundbreaking paradigm in quantum communications, enabling direct secure message transmission without pre-shared keys, thereby enhancing both security and efficiency. This work focuses on controller independent controlled bidirectional quantum secure direct communication (CICBQSDC), which allows legitimate users to establish confidential communication only after being authorized by the controller, while preventing the controller from accessing the communication content. Due to the persistent entanglement and stable self-associated structure of four-particle cluster states, we design a novel CICBQSDC protocol utilizing superdense encoding and four-particle cluster states, where one cluster state can exchange 4-bit messages with high efficiency. Furthermore, we rigorously prove the unconditional security of the designed protocol. The increased complexity of cluster states has historically hindered unconditional security proofs for such protocols. To the best of our knowledge, our protocol is the first cluster-state-based QSDC protocol that achieves provable unconditional security. This breakthrough not only validates our protocol’s security but also serves as a foundational reference for proving unconditional security in other cluster-state-based QSDC protocols.</p>