In the course of the revelations about both U.S. and European national surveillance programmes, remarkable constellations have come to light. Most national programmes are focused on the surveillance of IT-based communication among foreigners and between citizens and foreigners. This fact has often been employed as a mitigating argument within the national legal and policy discourses. This paper examines some of the possible loopholes and “dents” in the law that enable intelligence agencies to engage in international IT surveillance arbitrage. Fundamental rights currently do not protect against this practice. It leads to the factual circumvention of constitutional standards by permitting wider indirect access to domestic communication through processes of information sharing. We briefly assess possible legal answers to this phenomenon from the fields of public international law and global constitutionalism. Since international human rights law is merely territorial in focus it is incapable of constraining the above mentioned arbitrage practices. Territorial concepts of human rights protection are outdated with regards to international communication networks and ineffective for the legal regulation of state surveillance of these networks. We identify the universal legal principle of proportionality as the most promising starting point to structure and rationalise the legal debate on how to constrain international IT cross-surveillance.