A method for mitigating a 5G roaming attack using a security edge protection proxy (SEPP), includes receiving, at an SEPP, user equipment (UE) registration messages for outbound roaming subscribers. The method further includes creating, in a SEPP security database, UE roaming registration records derived from UE registration messages. The method further includes receiving, at the SEPP, a packet data unit (PDU) session establishment request message. The method further includes performing, using at least one parameter value extracted from the PDU session establishment request message, a lookup in the SEPP security database for a UE roaming registration record. The method further includes determining, by the SEPP and based on results of the lookup, whether to allow or reject the PDU session establishment request message.