Light Leak caused by Displacement Bump?

On the left is the only active light source in the scene, an area light outside of the room.
On the right is a shot from within the room. The bump details are somehow picking up the light from outside.

The material settings are only using the displacement as bump.
The face normals are pointing towards the inside of the room.
The material has no transparency, no alpha, no emission, and no translucency.

I can’t figure out why this is happening. My best guess is that it’s because of the displacement node.

How do I fix it?

Sometimes I have to create light blockers. Just dumb black objects to block light where there is none supposed to come through. It’s something that happens recurrently to me whenever I use geonodes to offset geometry like dropping ceiling rims or boards. Other than that I haven’t fought light leaks much.

If this started happening in 3.1 then it might be because of the removal of ray offsetting and it’s related commits.

That bug report has priority High, and it’s recognized as a regression, so it’ll be fixed in some release. Probably in the next bcon phase