Deubiquitinase involved in innate antiviral immunity by mediating deubiquitination of CGAS and RIGI (PubMed:31534008, PubMed:32027733). Negatively regulates RIGI by mediating 'Lys-63'- linked deubiquitination of RIGI, inhibiting type I interferon signaling (PubMed:32027733). Also regulates 'Lys-63'-linked ubiquitination level of MDA5/IFIH1 (PubMed:32027733). Acts as a positive regulator of the cGAS-STING pathway by catalyzing 'Lys-48'-linked deubiquitination of CGAS, thereby promoting its stabilization (PubMed:31534008). Can reduce the levels of BCL2L11/BIM ubiquitination and stabilize BCL2L11 in response to the RAF-MAPK-degradation signal (By similarity). By acting on BCL2L11 levels, may counteract the anti-apoptotic effects of MAPK activity (By similarity). {ECO:0000250|UniProtKB:Q8CEG8, ECO:0000269|PubMed:31534008, ECO:0000269|PubMed:32027733}. This is the function of USP27X (ubiquitin specific peptidase 27 X-linked, Ensembl gene identifier ENSG00000273820).