This paper addresses two reliability-based security threats and mitigations for embedded systems namely, aging and thermal side channels. Device aging can be used as a hardware attack vector by using voltage scaling or specially crafted instruction sequences to violate embedded processor guard bands. Short-term aging effects can be utilized to cause transient degradation of the embedded device without leaving any trace of the attack. (Thermal) side channels can be used as an attack vector and as a defense. Specifically, thermal side channels are an effective and secure way to remotely monitor code execution on an embedded processor and/or to possibly leak information.