Although not my area of strong expertise, I think I can say with confidence that terminating the stack inside the attic crawl space, either straight up or routed "towards the eaves" with rigid or flexible duct is absolutely unacceptable. Besides the condensation and leaking issue you now have, you have the distinct possibility of sewer gases up there. The main stack vent needs to terminate about 2 feet above the roof line. Probably need the help of a roofer to put this through, flash it, and get the shingle situation patched in.
How about some further comments from the "heavy guns" on this site!