Small e

If $e$ is sufficiently small, the exponent is ineffective at encrypting $m$.

Let's say $m^e<N$; in this case, we can simply take the $e$th root of $c$. For example, if $e=3$, then we can calculate $m = \sqrt[3]c$.

If $m^e > N$ then this is a bit more secure, but we can progressively add more multiples of $N$ until the cube root gives us a valid answer:

$$m = \sqrt[3]{c + kn}$$

Python

In Python we can use the gmpy3 iroot function:

from gmpy2 import iroot

m = iroot(ct, e)