Protease that acts as a positive regulator of the cGAS-STING pathway by catalyzing desumoylation of CGAS (PubMed:28095500). Desumoylation of CGAS promotes DNA-binding activity of CGAS, subsequent oligomerization and activation (PubMed:28095500). Deconjugates SUMO2 and SUMO3 from targeted proteins, but not SUMO1 (By similarity). Catalyzes the deconjugation of poly-SUMO2 and poly-SUMO3 chains (By similarity). Has very low efficiency in processing full-length SUMO proteins to their mature forms (By similarity). Belongs to the peptidase C48 family.