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Remote censorship measurement tools can now detect DNS- and IP-based blocking at global scale. However, a major unmonitored form of interference is blocking triggered by deep packet inspection of application-layer data. We close this gap by introducing Quack, a scalable, remote measurement system that can efficiently detect application-layer interference. We show that Quack can effectively detect application layer blocking triggered on HTTP and TLS headers, and it is flexible enough to support many other diverse protocols. In experiments, we test for blocking across 4458 autonomous systems, an order of magnitude larger than provided by country probes used by OONI. We also test a corpus of 100,000 keywords from vantage points in 40 countries to produce detailed national blocklists. Finally, we analyze the keywords we find blocked to provide insight into the application-layer blocking ecosystem and compare countries’ behavior. We find that the most consistently blocked services are related to circumvention tools, pornography, and gambling, but that there is significant country-to-country variation. 

We report the first wide-scale measurement study of server-side geographic restriction, or geoblocking, a phenomenon in which server operators intentionally deny access to users from particular countries or regions. Many sites practice geoblocking due to legal requirements or other business reasons, but excessive blocking can needlessly deny valuable content and services to entire national populations. To help researchers and policymakers understand this phenomenon, we develop a semi-automated system to detect instances where whole websites were rendered inaccessible due to geoblocking. By focusing on detecting geoblocking capabilities offered by large CDNs and cloud providers, we can reliably distinguish the practice from dynamic anti-abuse mechanisms and network-based censorship. We apply our techniques to test for geoblocking across the Alexa Top 10K sites from thousands of vantage points in 177 countries. We then expand our measurement to a sample of CDN customers in the Alexa Top 1M. We find that geoblocking occurs across a broad set of countries and sites. We observe geoblocking in nearly all countries we study, with Iran, Syria, Sudan, Cuba, and Russia experiencing the highest rates. These countries experience particularly high rates of geoblocking for finance and banking sites, likely as a result of US economic sanctions. We also verify our measurements with data provided by Cloudflare, and find our observations to be accurate.