Taking a (modified) page from Randaly’s book, I would define absolute certainty as “so certain that one cannot conceive of any possible evidence which might convince one that the belief in question is false”. Since you can conceive of the brain-in-the-vat scenario and believe that it is not impossible, I would say that you cannot be absolutely certain of anything, including the axioms and logic of the world you know (even the rejection of absolute certainty).
Taking a (modified) page from Randaly’s book, I would define absolute certainty as “so certain that one cannot conceive of any possible evidence which might convince one that the belief in question is false”. Since you can conceive of the brain-in-the-vat scenario and believe that it is not impossible, I would say that you cannot be absolutely certain of anything, including the axioms and logic of the world you know (even the rejection of absolute certainty).