Numbers 12:1

Amplified Bible

12 Now ^[a]Miriam and Aaron spoke against Moses because of the ^[b]Cushite woman whom he had married (for he had married a Cushite woman);

Numbers 12:1 Miriam is presumed to be the leader of the attack on Moses’ authority because she is mentioned before Aaron and because of the severity of her punishment.
Numbers 12:1 Because the ancient borders of Cush and Midian sometimes overlapped Miriam may have considered Moses’ wife, Zipporah, a Cushite instead of a Midianite (Ex 2:21); however, it is also possible that Zipporah had died and this refers to a second wife. Marriage with a Canaanite was forbidden (Ex 34:11, 16), but not marriage with an Egyptian or Cushite. Joseph’s wife was an Egyptian (Gen 41:45).