I don't think you need to worry. What would make short stints a red flag is if they're common -- having a single short stint early in your career is unlikely cause you difficulties.

Remember, the people considering your application are well aware of the realities of the workplace, and one of those realities is that every so often a job is just a bad fit. In those cases, leaving it sooner rather than later is a good thing for everybody concerned. When I'm looking over resumes, if I see someone who has generally worked for years at each position, but has a couple that only lasted a few months, I see that as perfectly normal.