A corner flashing system is provided for sealing the corners of recessed window frames against moisture penetration. In a preferred embodiment, the system comprises first and second double-flap members, a half-cube member, and caulking. The first and second double-flap members, and the half-cube member are preferably made of asphalt or petroleum based material. In another preferred embodiment, the system comprises one double-flap member, a modified half-cube member, and caulking. In another preferred embodiment, the system comprises a single member that combines a double-flap member and a half-cube member, and caulking. In another preferred embodiment, the system comprises a combination member, a double-flap member, and caulking.