I thought Fangorn was dangerous.

‘Dangerous!’ cried Gandalf. 'And so am I, very dangerous: more dangerous than anything you will ever meet, unless you are brought alive before the seat of the Dark Lord. And Aragorn is dangerous, and Legolas is dangerous. You are beset with dangers, Gimli son of Glóin; for you are dangerous yourself, in your own fashion. Certainly the forest of Fangorn is perilous — not least to those that are too ready with their axes; and Fangorn himself, he is perilous too; yet he is wise and kindly nonetheless.

I guess it’s up to interpretation, but personally I interpret that as dangerous as in lethality. Only Sauron had the power to best Gandalf the White in direct confrontation.