SuperMicro has posted an official BIOS update, v2.3a!
Go to the SuperMicro support page for your board (e.g., X9SCM-F or X9SCL-F). From the “Links & Resources” box on the right hand side, select “Update Your BIOS”. Links for both of these boards point to the same download zip; X9SCi and X9SCA have a different BIOS.