UFC President Dana White recently appeared on The Dan Le Batard Show. When asked about the possibility of a mixed martial arts fight between former UFC Heavyweight Champion and current WWE Universal Champion Brock Lesnar and former UFC Light Heavyweight Champion Jon "Bones" Jones, White revealed that his understanding is that Brock Lesnar's current WWE contract does not expire until August of 2018.
This contradicts some reports that stated that Lesnar's current WWE deal is set to expire shortly after WrestleMania 34 in April. If Dana White is correct then that means that Lesnar's WWE contract expires right around next year's SummerSlam.
White also mentioned that WWE has virtually no interest in ever letting Brock have another one-off fight in UFC again as long as he's under contract with WWE.