I notice that they have a magic attribute of one, which if reduced kill the cyberzombie instantly. Is there anything preventing a pc from casting a f 1 mana static spell and killing instantly?
You didn't read far enough. On the same page (emphasis added):
In effect, the cyberzombie becomes a domain in her own
right, tainting astral space around her wherever she goes. This astral
haze affects all attempts to cast magic on, at, or in the vicinity of
the cyberzombie.
Whatever the ambient mana conditions are, the
cyberzombie always stands at the heart of a Rating 4 background
count (see p. 117, Street Magic) that extends a number of meters
from her body equal to her total negative Essence. If she remains
in one place for long, that background count will expand at the
rate of about a meter in every direction every two or three hours.
So neither mana static, nor a mana void, nor a mana storm would do jack to a cyberzombie.
However, UmaroVI is right, being Dual Natured is the cyberzombie's real source of vulnerability. And it's a massive vulnerability.