Q. Is masah upon the khuffain permissible?

A. If Kuffain is being defined as leather socks, then yes, masah can be done over it, once an original ablution had been made.

If kuffain is defined as cotton socks that does not fulfill the durability of the leather socks as stipulated by the great Islamic jurists, then such a masah (wiping) would be invalid.

Allah certainly Knows Best.