Protease that acts as a positive regulator of the cGAS-STING pathway by catalyzing desumoylation of CGAS. Desumoylation of CGAS promotes DNA-binding activity of CGAS, subsequent oligomerization and activation (By similarity). Deconjugates SUMO2 and SUMO3 from targeted proteins, but not SUMO1 (PubMed:18799455). Catalyzes the deconjugation of poly-SUMO2 and poly-SUMO3 chains (PubMed:18799455). Has very low efficiency in processing full-length SUMO proteins to their mature forms (PubMed:18799455). Experimental confirmation may be lacking for some isoforms. Belongs to the peptidase C48 family.