Don't worry, it's legit. BioWare have freely released the soundtrack to Mass Effect 3's latest DLC pack, and you can pick it up on the BioWare Social Network. Note that you'll need to log into your Origin account (or existing BSN account) to do so.
If you're interested, I was utterly flabbergasted by how brilliant in our 9/10 Mass Effect 3: Citadel DLC review. It's like a holiday special that gets the whole cast back together, and gives you great new memories of Mass Effect 3 without compromising the ending in any way.