Mold in my basement on the rim joist

I have recently started finishing my basement and have a question for some knowledgeable people. First let me say I live in central WI and it is anywhere from 10 degrees to 30 this time of year. I live in a 4 year old house and recently started insulating the rim joists with 2" XPS foam. The builder had used fiberglass insulation to stuff in there when the house was built. After doing a number of rim joists without any problem I came across 4 in a row that had mold growing on the band joist.(pictures attached) Not a lot of mold but enough for me to take concern and want to fix it. I also noticed all 4 of the spaces that had mold also had rusted nails sticking through them from the outside nailed in.(I imagine the cold wicked through the nail to the warm air inside and condensated on the OSB) My basement is dry this time of year, my humidity gauge says 40% and the temp is 63 degrees with all the heat vents closed in the basement. The bare concrete walls measure around 55 degrees and the bare band joist is anywhere from 45-55 degrees. I talked to a worker at menards and he recommended i use Concrobium Mold Removal then seal it with a product called 1-2-3 which is a primer/sealer, then use the 2" foam and seal around it. I guess the whole point of my post is to see if I am doing things correctly or if I am missing something. any input is appreciated