Hybrid of "can" and "may"?

This question seems to be based on a false premise: that the word "can" is inappropriate whenever permission is involved. Despite what peevers would have you believe, the meaning of "can" is broad enough to cover various situations: see the answers to What is the difference between 'can', 'could', 'may' and 'might'? and Difference between "can" and "may". There is no need for a separate "hybrid" of can and may in contexts like the sentence that you have quoted. Can is perfectly all right here.

Can is the correct word. (And it doesn't seem like a hybrid to me.)

Nobody on Stack Exchange is granting or withholding you permission to vote more often. Whether you can or cannot is a simple fact that's built into the code on which the site runs.

If permission is granted or denied that means that it's capable of being granted or denied. Permission implies a decision resulting from a choice.

Here, the system has no choice. To infer permission would be a semantic mistake.