Vent pipe leaking in attic

[HuntingtonToothman]

I have a leak where a vent pipe from a bathroom joins the vent stack. It suddenly started a week ago and is steady. We have had no rain for two weeks. I don't know how water could up to the joint in the attic. See picture. Any ideas?

 

[Mr_David]

can't see the water but does it look like beads of water on pipe?
Just a guess but it could be condensation.
If you have a lot of moisture in your air and it is getting cold outside, It is possible that the warm are from a hot shower is rising in the vent causing the cool moist air to condensate on the vent pipe