A natural 1 on the confirmation roll automatically fails to confirm the critical hit
On Critical Hits, in part, says, "To find out if [a threat is] a critical hit, you immediately make an attempt to 'confirm' the critical hit—another attack roll with all the same modifiers as the attack roll you just made. If the confirmation roll also results in a hit against the target’s AC, your original hit is a critical hit." (emphases mine).
On Automatic Hits and Misses, in part, says, "A natural 1 (the d20 comes up 1) on an attack roll is always a miss."
Thus, because the roll to confirm a critical hit is an attack roll, the roll to confirm automatically misses on a natural 1, and the attack is a normal hit rather than a critical hit.