Stop Our Scourge Act of 2023 or the SOS Act of 2023 This bill directs the Department of Homeland Security to designate illicit fentanyl as a weapon of mass destruction and requires the Office of National Drug Control Policy to conduct an assessment regarding that substance. Specifically, the office must assess foreign manufacturing of illicit fentanyl, the tools and capabilities across federal agencies to address trafficking of that substance, the capabilities of the Mexican military to conduct counterdrug missions with respect to that substance, the capacities and willingness of China to take specified actions with respect to that substance, and illicit fentanyl being trafficked into the United States from Mexico.