Satellite networks are essential to global connectivity yet face severe multidimensional cybersecurity threats. This systematic review conducts a holistic analysis of threats across the physical, network, and user layers. We propose the Sat-ATT&CK knowledge matrix to model satellite-specific attack chains. Corresponding defense technologies are organized within the core functions (Protect, Detect, Respond) of the National Institute of Standards and Technology (NIST) Cybersecurity Framework, establishing a structured threat–defense mapping. Furthermore, an exploratory case study on fine-tuning a large language model (SatSec) using the compiled literature corpus is presented. Finally, we identify key challenges and outline the future research directions toward a more resilient and intelligent security paradigm.