DIAGNOSIS Over-tightening the blade assembly onto the cup, or a drop that stressed that threaded area, caused a hairline crack. It's a weak point on a lot of these models.
FIX Yes, you can buy replacement cups. They're sold as accessories. Search for "Ganiza blender replacement cup" or "17oz travel cup" to find the right size. Make sure the threading matches. You don't need a whole new blender.
IF THAT DIDN'T WORK If you can't find the exact branded cup, generic cups might not thread on correctly or seal properly. Check the product listing or manual for the specific thread pattern or cup model number.
HEADS UP When you screw the blade base on, hand-tighten it until it's snug, then maybe a quarter-turn more. Don't crank it with all your might. The seal comes from the silicone gasket, not extreme torque, and cranking it is what cracks the plastic.