  We present a novel approach to deal with transitivity permission-delegation
threats that arise in social networks when content is granted permissions by
third-party users thereby breaking the privacy policy of the content owner.
These types of privacy breaches are often unintentional in social networks like
Facebook, and hence, (more) in-place mechanisms are needed to make social
network users aware of the consequences of changing their privacy policies. Our
approach is unique in its use of formal methods tools and techniques. It builds
on a predicate logic definition for social networking that caters for common
aspects of existing social networks such as users, social network content,
friendship, permissions over content, and content transmission. Our approach is
implemented in Yices. For the predicate logic model, we formulate a security
policy for the verification of the permission flow of content owned by social
network users and demonstrate how this security policy can be verified.
