Open WebUI is a self-hosted artificial intelligence platform designed to operate entirely offline. Prior to 0.9.0, the POST /api/v1/models/import endpoint allows users with the workspace.models_import permission to overwrite any existing model in the database, regardless of ownership. When an imported model's ID matches an existing model, the endpoint merges the attacker's payload over the existing model data and writes it to the database with no ownership or access grant validation. Additionally, filter_allowed_access_grants is never called, bypassing the access grant restrictions enforced on all other model mutation endpoints. This vulnerability is fixed in 0.9.0.