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. Catalyzes the deconjugation of poly-SUMO2 and poly-SUMO3 chains. Has very low efficiency in processing full-length SUMO proteins to their mature forms (By similarity). Belongs to the peptidase C48 family.