Necessary in itself (wājib al-wujūd li-dhātih) describes a being whose existence does not depend upon another. An attribute's being necessarily true of that essence does not give the attribute independent necessary existence.
Knowledge and life are eternal and inseparable divine perfections, yet knowledge is not a separate essence that exists through its own independent necessity.
Thus one must distinguish necessity meaning self-subsistent existence from the necessary belonging of an attribute to its subject. Confusing these senses creates the mistaken claim that affirming necessary attributes multiplies necessary beings.