Pathfinder

So far, existing censorship studies have largely focused on country-level characterization, primarily because (1) censorship enforcement is often mandated through nationwide policies and (2) it is difficult to control the routing of probing packets to trigger censorship across different networks within a country. However, censorship mechanisms can vary significantly at the ISP level, revealing a more diverse landscape than previously assumed.

We bridge this gap by conducting an in-depth investigation to scrutinize the inconsistency of censorship enforcement within a country. We design and deploy Pathfinder, a measurement framework to uncover inconsistent censorship behavior across different network paths. Pathfinder leverages multiple geo-distributed back-end control servers as probing destinations to induce routing variability. Specifically, by issuing probing packets from a single vantage point to multiple geo-distributed destinations, we can force the traffic to traverse different transit networks, enabling the detection of inconsistent censorship enforcement across various networks.

Our large-scale experiments and analysis reveal that diverse censorship resulting from varying routing paths within a country is widespread, implying that (1) the implementations of centralized censorship are commonly incomplete or flawed and (2) decentralized censorship is also prevalent. Moreover, we find that different hosting platforms also contribute to inconsistent censorship behavior due to their varying peering relationships with ISPs within a country. We also present detailed case studies to illustrate the configurations that lead to such inconsistencies and to explore their underlying causes.

Relevant Papers

Xiaoqin Liang, Guannan Liu, Lin Jin, Shuai Hao, and Haining Wang. Pathfinder: Exploring Path Diversity for Assessing Internet Censorship Inconsistency, in the 41st Annual Computer Security Applications Conference (ACSAC), December 2025.