A baseband processor is a dedicated chip or subsystem that handles cellular radio functions separately from the main application processor. It manages signal processing, network registration, voice and data links, and low-level modem behavior, often through its own firmware and memory. Because it sits between the device and the mobile network, it operates as a distinct trust domain with direct control over radio communications.
This matters in cyber security because baseband firmware can be attacked independently of the operating system. Researchers and attackers may target it with malformed radio messages, rogue network signals, or command paths exposed through SIM and modem features. If the baseband is compromised, an attacker may disrupt connectivity, intercept traffic metadata, or influence the wider device depending on how tightly the modem is isolated. Defenders reduce risk by keeping modem firmware updated, limiting unnecessary SIM-toolkit and AT-command exposure, and treating the cellular module as sensitive infrastructure rather than a simple peripheral.