It is a free ball.
This is from the rules:
The cue-ball is said to be snookered when a direct stroke in a straight line to
every ball on is wholly or partially obstructed by a ball or balls not on. If one or
more balls on can be struck at both extreme edges free of obstruction by any
ball not on, the cue-ball is not snookered.
(a) If in-hand, the cue-ball is snookered if it is obstructed as described above
from all possible positions on or within the lines of the “D”.