> Currently there is no a bug in ast.literal_eval() because the '**' operator is not accepted.

The doc says "This can be used for safely evaluating strings containing Python values from untrusted sources without the need to parse the values oneself. It is not capable of evaluating arbitrarily complex expressions, for example involving operators or indexing."
https://docs.python.org/dev/library/ast.html#ast.literal_eval

I don't think that it's a bug, but a deliberate design choice. a**b is an obvious trick to DoS a server (high CPU and memory usage).