The cube's UV layout is arranged in a 3×2 layout that allows texturing each face individually. To apply the same texture on all faces, change the material's UV property to [code]Vector3(3, 2, 1)[/code].
[b]Note:[/b] When using a large textured [CubeMesh] (e.g. as a floor), you may stumble upon UV jittering issues depending on the camera angle. To solve this, increase [member subdivide_depth], [member subdivide_height] and [member subdivide_width] until you no longer notice UV jittering.