Abstract: The bacterial CBASS(cyclic-oligonucleotide-based anti-phage signaling system) represents a novel innate immune defense mechanism mediated by cyclic nucleotides.The system employs cGAS/DncV-like nucleotidyltransferases (CD-NTases) to recognize exogenous nucleic acids, catalyzing the production of second messenger molecules such as cyclic GMP-AMP (cGAMP) to activate effector proteins (e.g., nucleases), thereby triggering "cell suicide" to combat phage infection. The molecular mechanisms and evolutionary features of CBASS not only uncover the diversity of bacterial immune defenses but also provide critical insights into the conservation of prokaryotic-eukaryotic immune pathways. Notably, the bacterial CBASS system exhibits profound homology with the eukaryotic cGAS-STING (Cyclic GMP-AMP Synthase—Stimulator of Interferon Genes) pathway across multiple dimensions, including the catalytic domains of CD-NTase/cGAS and cyclic nucleotide signaling mechanisms. This finding supports the hypothesis that eukaryotic innate immunity may have originated from prokaryotic horizontal gene transfer and highlights an evolutionary shift in defense strategies from bacterial "population lysis" to "individual inflammatory activation" in higher organisms.This review systematically synthesizes the functional architecture and mechanisms of the CBASS system, with a deep exploration of its evolutionary connections to the eukaryotic cGAS-STING pathway. The insights gained herein offer fresh perspectives for understanding the origin and evolution of the innate immune system, and for driving advancements in biotechnological research and development.