An aux input is a line-level audio port, usually a 3.5 mm jack, that accepts an external sound signal from another device. On speakers, radios, assistants, and embedded systems, it provides a simple wired path for audio playback without using a network connection.
In cyber security, an aux input matters because it is a physical trust boundary. Anything connected to it can influence how the device behaves, so firmware must correctly route, filter, and disable the port when needed. Attackers may abuse external audio paths to inject unwanted audio, trigger voice interfaces, or bypass expectations about what the device should hear. Defenders reduce risk by disabling unused inputs, validating firmware updates, and testing how hardware reacts after software changes. Even a basic audio jack can become a security-relevant control point when a connected product depends on software to manage it.