Leveraging DNS for covert communications is appealing since most networks allow DNS traffic, especially the ones directed toward renowned DNS hosting services. Unfortunately, most DNS hosting services overlook domain ownership verification, enabling miscreants to host undelegated DNS records of a domain they do not own. Consequently, miscreants can conduct covert communication through such undelegated records for whitelisted domains on reputable hosting providers. In this paper, we shed light on the emerging threat posed by undelegated records and demonstrate their exploitation in the wild. To the best of our knowledge, this security risk has not been studied before.

HTTPS secures communications in the web and heavily relies on the Web PKI for authentication. In the Web PKI, Certificate Authorities (CAs) are organizations that provide trust and issue digital certificates. Web clients rely on public root stores maintained by operating systems or browsers, with hundreds of audited CAs as trust anchors. However, as reported by security incidents, hidden root CAs beyond the public root programs have been imported into local root stores, which allows adversaries to gain trust from web clients.

Illicit traffic monetization is a type of Internet fraud that hijacks users' web requests and reroutes them to a traffic network (e.g., advertising network), in order to unethically gain monetary rewards. Despite its popularity among Internet fraudsters, our understanding of the problem is still limited. Since the behavior is highly dynamic (can happen at any place including client-side, transport-layer and server-side) and selective (could target a regional network), prior approaches like active probing can only reveal a small piece of the entire ecosystem. So far, questions including how this fraud works at a global scale and what fraudsters' preferred methods are, still remain unanswered. To fill the missing pieces, we developed TraffickStop the first system that can detect this fraud passively. Our key contribution is a novel algorithm that works on large-scale DNS logs and efficiently discovers abnormal domain correlations. TraffickStop enables the first landscape study of this fraud, and we have some interesting findings. By analyzing over 231 billion DNS logs of two weeks, we discovered 1,457 fraud sites. Regarding its scale, the fraud sites receive more than 53 billion DNS requests within one year, and a company could lose up to 53K dollars per day due to fraud traffic. We also discovered two new strategies that are leveraged by fraudsters to evade inspection. Our work provides new insights into illicit traffic monetization, raises its public awareness, and contributes to a better understanding and ultimate elimination of this threat.

DNS packets are designed to travel in unencrypted form through the Internet based on its initial standard. Recent discoveries show that real-world adversaries are actively exploiting this design vulnerability to compromise Internet users' security and privacy. To mitigate such threats, several protocols have been proposed to encrypt DNS queries between DNS clients and servers, which we jointly term as DNS-over-Encryption. While some proposals have been standardized and are gaining strong support from the industry, little has been done to understand their status from the view of global users.

Internationalized Domain Names (IDNs) are domain names containing non-ASCII characters. Despite its installation in DNS for more than 15 years, little has been done to understand how this initiative was developed and its security implications. In this work, we aim to fill this gap by studying the IDN ecosystem and cyber-attacks abusing IDN. In particular, we performed by far the most comprehensive measurement study using IDNs discovered from 56 TLD zone files. Through correlating data from auxiliary sources like WHOIS, passive DNS and URL blacklists, we gained many insights. Our discoveries are multi-faceted. On one hand, 1.4 million IDNs were actively registered under over 700 registrars, and regions within east Asia have seen prominent development in IDN registration. On the other hand, most of the registrations were opportunistic: they are currently not associated with meaningful websites and they have severe configuration issues (e.g., shared SSL certificates). What is more concerning is the rising trend of IDN abuse. So far, more than 6K IDNs were determined as malicious by URL blacklists and we also identified 1,516 and 1,497 IDNs showing high visual and semantic similarity to reputable brand domains (e.g., apple.com). Meanwhile, brand owners have only registered a few of these domains. Our study suggests the development of IDN needs to be re-examined. New solutions and proposals are needed to address issues like its inadequate usage and new attack surfaces.