Growing levels of digitalization and broadband access drives extremely fast progress in multimedia and networking technologies and allows consumers to create requirements at an accelerating rate. Producers? response is to emphasize the speed of delivery and upgradability of applications. Development of Web Services and Service-Oriented Architecture puts the emphasis on creation of specific services which then can be aggregated to achieve a particular goal. By substituting or adding new services, a particular application can be adapted faster to changing requirements. Any application thus composed must address security concerns, including security guarantees after a service substitution. Based on our framework for creating multimedia collaborative authoring applications from a set of standard services, we provide a security analysis of the resulting application and present a novel framework for ensuring uniform access control guarantees across different constituent services.