By handling the orchestration, composition and interaction of Web services, the Business Process Execution Language (BPEL) has gained tremendous interest. However, such process-based language does not assure a secure environment for Web services composition. The key solution cannot be seen as a simple embed of security properties in the source code of the business logic since the dynamism of the BPEL process will be affected when the security measures get updated. In this context, several approaches have emerged to tackle such issue by offering the ability to specify the security properties independently from the business logic based on policy languages. Nevertheless, these languages are complex, verbose and require programming expertise. Owing to these difficulties, specifying and the enforcing BPEL security policies become very tedious tasks. To mitigate these challenges, we propose in this paper, a novel approach that takes advantage of both the Unified Modeling Language (UML) and the Aspect Oriented Paradigm (AOP). By elaborating a UML extension mechanism, called UML Profile, our approach provides the users with model-based capabilities to specify aspects that enforce the required security policies. On the other hand, it offers a high level of flexibility when enforcing security hardening solutions in the BPEL process by exploiting the AOP approach. We illustrate our approach through an example of the dynamic generation and integration of model-based security aspects in a BPEL process.