Personally, I think you should get out of there before your brain turns to mush and falls out. Other posters are telling you to instead perceive it as a blessing to work on these things that you find mundane and boring, but I strongly disagree. To quote Paul Graham, "If you're worried that your current job is rotting your brain, it probably is."
Don't quit, but start applying/interviewing for a new job. You will need to have a good explanation for why you're looking for a new job so quickly after starting, but that's doable. You're in a pretty strong position if you start interviewing for new jobs before quitting -- at least that makes it clear that you weren't fired, and it'll sound credible when you tell them that you're just not challenged enough by your current job.