Micro-Policies for Web Session Security

Micro-policies, originally proposed to implement hardware-level security monitors, constitute a flexible and general enforcement technique, based on assigning security tags to system components and taking security actions based on dynamic checks over these tags. In this paper, we present the first application of micro-policies to web security, by proposing a core browser model supporting them and studying its effectiveness at securing web sessions. In our view, web session security requirements are expressed in terms of a simple, declarative information flow policy, which is then automatically translated into a micropolicy enforcing it. This leads to a browser-side enforcement mechanism which is elegant, sound and flexible, while being accessible to web developers. We show how a large class of attacks against web sessions can be uniformly and effectively prevented by the adoption of this approach. We also develop a proof-of-concept implementation of a significant core of our proposal as a Google Chrome extension, Michrome: our experiments show that Michrome can be easily configured to enforce strong security policies without breaking the functionality of websites.