Cur rescues are often thought to be Boxer mixes. Yours could very well be a BMC. Look for the dark pigment on the lips, inside the mouth, gums and throat but not the tongue. Many Curs are born with bob tails, as yours might be. The combination of BMC traits and the bob tail makes me think this dog has to be a BMC.
AWW so cute. I have had 2 Boxers, yes he is part Boxer-- look at his square build and that black mask/ black muzzle, the tan coloration-- all Boxer-- to me he looks remarkedly like my Boxer Boy as a Pup. They are grt dogs have Fun!