Covert channel attack is an attack that happens due to side channel exploitation. In addition, It is a type of cyberattack that creates the capability of transferring information objects between processes that could have been otherwise impossible to occur through the overt channels. It is some sort of timing, storage, etc. attack
A covert channel of communication is a channel that is not designed or intended to transfer information through it. Unlike overt channel, covert channel is mostly used for malicious activities and hence not protected by the security controls in place. The purpose of this attack is to circumvent and bypass security controls and policies that cloud have been impossible to achieve through direct over channels. Covert channel attack is common attack in storage systems and electrical power systems.