Web applications are widely adopted and their correct functioning is mission critical for many businesses. At the same time, Web applications tend to be error prone and implementation vulnerabilities are readily and commonly exploited by attackers. The design of countermeasures that detect or prevent such vulnerabilities or protect against their exploitation is an important research challenge for the fields of software engineering and security engineering. In this paper, we focus on one specific type of implementation vulnerability, namely, broken dependencies on session data. This vulnerability can lead to a variety of erroneous behavior at runtime and can easily be triggered by a malicious user by applying attack techniques such as forceful browsing. This paper shows how to guarantee the absence of runtime errors due to broken dependencies on session data in Web applications. The proposed solution combines development-time program annotation, static verification, and runtime checking to provably protect against broken data dependencies. We have developed a prototype implementation of our approach, building on the JML annotation language and the existing static verification tool ESC/Java2, and we successfully applied our approach to a representative J2EE-based e-commerce application. We show that the annotation overhead is very small, that the performance of the fully automatic static verification is acceptable, and that the performance overhead of the runtime checking is limited.

Unanticipated software adaptations are becoming increasingly important in the domain of distributed systems. Due to performance and availability requirements, these adaptations need to be enforced at run-time. However for dynamic changes to yield valid systems, a safe state for reconfiguration of the involved software modules must be enforced. This paper proposes a solution to modularize support for achieving safe reconfiguration and separate it from basic application functionality. In addition, we describe a mechanism to obtain a safe state for unanticipated reconfiguration of producer/consumer based systems, rather than being limited to updates of independent software components. The presented method imposes such a safe state with minimal interference to the rest of the system, and with minimal contribution from the programmer. We believe that a wide range of producer/consumer based systems can take advantage of the presented solution.

Research domains such as active networks, ad-hoc networks, ubiquitous computing, pervasive computing, grid computing, and sensor networks, clearly show that computer networks will become more complex and heterogeneous. In many cases, central management and control of the network are far from trivial since both the topology and the connected devices change rapidly in such highly dynamic environments, while load circumstances may vary arbitrarily. The software architecture in a node needs to support flexibility. We have developed an architecture tailored to protocol stack software that allows customizing internal resource management in order to handle overload conditions gracefully. We show that the investment in explicit support for modularity and architectural constraints pays off: the paper elaborates on a case study in which dynamic adaptation of access control behavior leads to significant performance improvements.

This paper discusses client-specific customization of systems that implement an on-line Internet service in the presence of simultaneous client-specific views. The problem is that each client must be able to customize the running system for use in its own context, without impacting the service behavior that is delivered to other clients. To solve this, we propose to customize the system on a per client request basis, where the system itself consists of a stable core and several extensions that are injected into the core as needed. However, this approach brings on its own several consistency management problems that must be dealt with in order to make the approach viable. We give an overview of these problems and present a management architecture that deals with these problems.

In this position paper we unify three essential features for flexible system software: a component oriented approach, self-adaptation and separation of concerns. We propose DiPS (Distrinet Protocol Stack), a component framework, which offers components, an anonymous interaction model and connectors to handle non-functional aspects such as concurrency.

Support for dynamic and client-specific customization is required in many application areas. We present a (distributed) application as consisting of a minimal functional core, implemented as a component based system, and an unbound set of potential extensions that can be selectively integrated within this core functionality. An extension to this core may be a new service due to new requirements of end users. Another important category of extensions we consider are non-functional services such as authentication, which typically introduce interaction refinements at the application level. In accordance with the separation of concerns principle, each extension is implemented as a layer of mixin-like wrappers. Each wrapper incrementally adds behavior and state to a core component instance from the outside, without modifying the component's implementation. The novelty of this work is that the composition logic, responsible for integrating extensions into the core system, is externalized from the code of clients, core system and extensions. Clients (end users, system integrators) can customize this composition logic on a per collaboration basis by 'attaching' high-level interpretable extension identifiers to their interactions with the core system.