ownership chaining, and it's the default behavior.
if you grant EXECUTE on a procedure to a user with no other permissions, as long as the stored procedure only touches objects in the same schema(dbo, probably) and in the same database,
the procedure will perform and execute it's code on it's underlying objects udner the context of the owner...insert,update, delete and more, even to objects the end user doesn't even know exist.
this is specifically so end users don't need permissions to the actual tables themselves.
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