Smart cities are emerging and comprise a plethora of interconnected devices, there-fore, the provision of security and privacy is challenging. This paper highlightsa brief review of security threats and challenges faced by smart cities and theirapplications. The interconnectivity and the complex heterogeneity between thephysical and cyberinfrastructure of smart cities require special security countermea-sures. The architecture of smart cities is discussed followed by the various attacksat Network, Perception, and Application layers. Overall, this review paper serves asa valuable resource and reference point for academia and industrial practitioners