If a user is granted write permissions to a directory, the user has the privilege to manage permissions of every entry in that directory. This privilege includes the assignment of read-, write- and execute permissions on every file and directory contained in that directory.
By extension, the user could also gain every permission to every file inside a subdirectory: The user could assign write permissions for the subdirectory and then proceed to manage the permissions of the files contained therein. This means that if a user has effective write permissions on a directory, that user also has potential read-, write- and execute-permissions on every file and directory in that directory and any of its subdirectories. Those permissions might not be immediately effective, but the user can gain them at any desired time.