User blog comment:The Bespectacled Guy/On World of Remnant 2/@comment-10380701-20140919000337/@comment-5217560-20140921013221

Or perhaps Beacon just isn't that strict on security. Cinder being able to infiltrate as a student at Beacon is actually pretty solid. For one, she and the other two are just there for a few days, like Sun and the others, and are from a different schools that most likely just provided a list of their students to Beacon(with Cinder and Co. getting on said list). So there probably wasn't a need to meticously search their background. Also, this is a festival celebrating a "time of peace" so under that idealogy, Ozpin and the other staff members most likely didn't feel the need to execute additiontional secruity measures. Wise? no. Understandable? Perhaps.