The two primary documents regarding legal niceties on the Moon and often mentioned are:
Outer Space Treaty of 1967, which according to Wikipedia is essentially ratified by any country with a chance of getting there
Moon Treaty which according to Wikipedia is NOT ratified by any country with a chance of getting there and such has negligible influence.
The Outer Space Treaty of 1967, seems to prohibit land ownership (Article II; "is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.") and Article VI puts all non-governmental entities under the control and responsibility of their home country. This would seem to preclude land ownership.
Questions of a legal opinion are out of scope here. This question relates solely to the existence of other documents and treaties.
Are there any other documented agreements or treaties between a majority of the nations which have the technologies to travel into space which would allow for, or do not specifically prohibit owning land on the moon?