  Covert channel attacks represent a significant threat to system security,
leveraging shared resources to clandestinely transmit information from highly
secure systems, thereby violating the system's security policies. These attacks
exploit shared resources as communication channels, necessitating resource
partitioning and isolation techniques as countermeasures. However, mitigating
attacks exploiting modern processors' hardware features to leak information is
challenging because successful attacks can conceal the channel's existence. In
this paper, we unveil a novel covert channel exploiting the duty cycle
modulation feature of modern x86 processors. Specifically, we illustrate how
two collaborating processes, a sender and a receiver can manipulate this
feature to transmit sensitive information surreptitiously. Our live system
implementation demonstrates that this covert channel can achieve a data
transfer rate of up to 55.24 bits per second.
