It could be, unfortunately. The only to get at it, is a full CLA. The one thing to try first, is removing the front and read elements -- they unscrew as a group -- and thoroughly blow off the outside surface of those inside elements. Hopefully it's dust there and you'll be done. If not, and it is on the surfaces inside the groups themselves, it's likely fungus...The one question mark is the "stuff" on one of the lens elements. I have taken some snaps to try to show what it looks like. The lens doesn't actually get foggy as it looks like in the third photo, that is just something to do with the angle and the light reflected off the table behind. In general, it looks a little like there is some dense dust in there, especially around the edges, but no spider webs. I am wondering if it might be the early stages of fungus.
FWIW, lens fungus is contagious, so whatever you do, do NOT store that lens with your other lenses!