I haven't seen the movie, but in the Book, he wasn't aware that the Cabinet was how they got in, nor, necessarily, the full nature of the Room of Requirement.
He mentions the room in GoF -
"...I took a wrong turn on the way to the bathroom and found myself in a beautifully proportioned room I had never seen before, containing a really rather magnificent collection of chamberpots. When I went back to investigate more closely, I discovered that the room had vanished. But I must keep an eye out for it. Possibly it is only accessible at five thirty in the morning. Or it may only appear at the quarter moon - or when the seeker has an exceptionally full bladder."
It's possible he knew more about it (Pottermore indicates he got the Mirror of Erised there).. but not certain. He doesn't seem surprised by the reference to it, tho, when Malfoy explains how he got Death Eaters into Hogwarts. He DOES however reveal that he didn't know about the cabinet.
“But why? I don’t think you will kill me, Draco. Killing is not nearly as easy as the innocent believe… so tell me, while we wait for your friends… how did you smuggle them in here? It seems to have taken you a long time to work out how to do it.”
...
Then, as though he could not help himself, he said, “I had to mend that broken Vanishing Cabinet that no one’s used for years. The one Montague got lost in last year.”
Dumbledore’s sigh was half a groan. He closed his eyes for a moment.
“That was clever… there is a pair, I take it?”
...
“Very good,” murmured Dumbledore. “So the Death Eaters were able to pass from Borgin and Burkes into the school to help you… a clever plan, a very clever plan… and, as you say, right under my nose…”
