For ensuring a universal serial bus, USB, attack protection between a communication device (CD) and an accessory device (AD), a protection device (PD) being inserted between the communication device (CD) and the accessory device (AD) through a USB link, the communication device (CD): memorizes the highest value (HV) of indexes of string descriptor found in a USB Device Descriptor received from the accessory device (AD), sends a request (Req) for a string descriptor to the accessory device (AD) with a value (Val1) of index higher than said highest value (HV), receives a response (Res) generated and sent from the protection device (PD), the response containing an identifier (Id P) of the protection device validates the presence of the protection device (PD) if the identifier (Id P) is found in a database.