When you register a new asset, the Edgemesh backend downloads it from origin itself to validate the hash you've calculated. And on replication the destination recalculates it on the payload (to make sure the asset replicated correctly).
I get an edgemesh site to accept file A (perhaps the site allows me to upload a user avatar, upload an image on a forum, etc). I then behave as a node in the mesh, and receive file A. When I get a request to replicate file A to someone else, I send them file A', they check the MD5 hash, and the hash matches. Not seeing how that doesn't work?
It is admittedly a narrow attack, but I think it works.