In 2015, we released Censys to lower the barrier to entry for researchers to study Internet devices by continually collecting and packaging Internet scan data. Since then, as we have learned more about how best to capture the complex behavior of Internet services and begun to serve commercial and government users, we have re-architected every aspect of how Censys operates. Motivated by requests from the community,we present Censys' evolution and current architecture, evaluate its visibility, and detail how Censys has been used by research, industry, and government. Finally, informed by our operational experiences, we discuss unsolved problems and the lessons we have learned. We hope that our work provides the transparency needed for researchers to soundly use Censys data and offers directions for future research.

This paper empirically evaluates the efficacy of two ubiquitous forms of enterprise security training: annual cybersecurity awareness training and embedded anti-phishing training exercises. Specifically, our work analyzes the results of an 8-month randomized controlled experiment involving ten simulated phishing campaigns sent to over 19,500 employees at a large healthcare organization. Our results suggest that these efforts offer limited value. First, we find no significant relationship between whether users have recently completed cybersecurity awareness training and their likelihood of failing a phishing simulation. Second, when evaluating recipients of embedded phishing training, we find that the absolute difference in failure rates between trained and untrained users is extremely low across a variety of training content. Third, we observe that most users spend minimal time interacting with embedded phishing training material in-the-wild; and that for specific types of training content, users who receive and complete more instances of the training can have an increased likelihood of failing subsequent phishing simulations. Taken together, our results suggest that anti-phishing training programs, in their current and commonly deployed forms, are unlikely to offer significant practical value in reducing phishing risks.

Enterprise-scale mandatory password changes are disruptive, complex endeavors that require the entire workforce to prioritize a goal that is often secondary to most users. While ample literature exists around user perceptions and struggles, there are few “best practices” from the perspective of the enterprise—either to achieve the end goal or to minimize IT costs. In this paper, we provide an empirical analysis of an enterprise-scale mandatory password change, covering almost 10,000 faculty and staff at an academic institution. Using a combination of user notifications logs, password update records, and help desk ticket information, we construct an empirical model of user response over time. In particular, we characterize the elements of the campaign that relate to ideal and non-ideal outcomes, including unnecessary user actions and IT help desk overhead. We aim to provide insight into successes and challenges that can generalize to other organizations implementing similar initiatives.

The critical role played by email has led to a range of extension protocols (e.g., SPF, DKIM, DMARC) designed to protect against the spoofing of email sender domains. These protocols are complex as is, but are further complicated by automated email forwarding — used by individual users to manage multiple accounts and by mailing lists to redistribute messages. In this paper, we explore how such email forwarding and its implementations can break the implicit assumptions in widely deployed anti-spoofing protocols. Using large-scale empirical measurements of 20 email forwarding services (16 leading email providers and four popular mailing list services), we identify a range of security issues rooted in forwarding behavior and show how they can be combined to reliably evade existing anti-spoofing controls. We further show how these issues allow attackers to not only deliver spoofed email messages to prominent email providers (e.g., Gmail, Microsoft Outlook, and Zoho), but also reliably spoof email on behalf of tens of thousands of popular domains including sensitive domains used by organizations in government (e.g., state.gov), finance (e.g., transunion.com), law (e.g., perkinscoie.com) and news (e.g., washingtonpost.com) among others.

E-mail has long been a critical component of daily communication and the core medium for modern business correspondence. While traditionally e-mail service was provisioned and implemented independently by each Internet-connected organization, increasingly this function has been outsourced to third-party services. As with many pieces of key communications infrastructure, such centralization can bring both economies of scale and shared failure risk. In this paper, we investigate this issue empirically --- providing a large-scale measurement and analysis of modern Internet e-mail service provisioning. We develop a reliable methodology to better map domains to mail service providers. We then use this approach to document the dominant and increasing role played by a handful of mail service providers and hosting companies over the past four years. Finally, we briefly explore the extent to which nationality (and hence legal jurisdiction) plays a role in such mail provisioning decisions.

Governments around the world enacted stay-at-home orders in response to the COVID-19 pandemic, which changed many aspects of life, including how people interacted with the Internet. These draconian restrictions on in-person social interactions were perhaps most acutely felt by people living alone. We study the changes in network traffic of one such population, students remaining in the (single-occupancy) on-campus dormitories at a large residential educational institution during the onset and initial few months of the lock-down. Specifically, we analyze how students shifted their online work and leisure behaviors at an application level. Further, we segment the population into domestic and international students, and find that even within these two broad sub-populations, there are significant differences in Internet-based behavior. Our work provides a focused lens on pandemic Internet usage, examining both 1) a concentrated user population and 2) the differing impacts of a global pandemic on disparate sub-populations.

“Serverless” cloud services, such as AWS lambdas, are one of the fastest growing segments of the cloud services market. These services are popular in part due to their light-weight nature and flexibility in scheduling and cost, however the security issues associated with serverless computing are not well understood. In this work, we explore the feasibility of constructing a practical covert channel from lambdas. We establish that a fast co-residence detection for lambdas is key to enabling such a covert channel, and proceed to develop a reliable and scalable co-residence detector based on the memory bus hardware. Our technique enables dynamic discovery for co-resident lambdas and is incredibly fast, executing in a matter of seconds. We evaluate our approach for correctness and scalability, and use it to establish covert channels and perform data transfer on AWS lambdas. We show that we can establish hundreds of individual covert channels for every 1000 lambdas deployed, and each of those channels can send data at a rate of 00 bits per second, thus demonstrating that covert communication via lambdas is entirely feasible.

Security is a discipline that places significant expectations on lay users. Thus, there are a wide array of technologies and behaviors that we exhort end users to adopt and thereby reduce their security risk. However, the adoption of these "best practices" --- ranging from the use of antivirus products to actively keeping software updated --- is not well understood, nor is their practical impact on security risk well-established. This paper explores both of these issues via a large-scale empirical measurement study covering approximately 15,000 computers over six months. We use passive monitoring to infer and characterize the prevalence of various security practices in situ as well as a range of other potentially security-relevant behaviors. We then explore the extent to which differences in key security behaviors impact real-world outcomes (i.e., that a device shows clear evidence of having been compromised).

Email accounts represent an enticing target for attackers, both for the information they contain and the root of trust they provide to other connected web services. While defense-in-depth approaches such as phishing detection, risk analysis, and two-factor authentication help to stem large-scale hijackings, targeted attacks remain a potent threat due to the customization and effort involved. In this paper, we study a segment of targeted attackers known as “hack for hire” services to understand the playbook that attackers use to gain access to victim accounts. Posing as buyers, we interacted with 27 English, Russian, and Chinese blackmarket services, only five of which succeeded in attacking synthetic (though realistic) identities we controlled. Attackers primarily relied on tailored phishing messages, with enough sophistication to bypass SMS two-factor authentication. However, despite the ability to successfully deliver account access, the market exhibited low volume, poor customer service, and had multiple scammers. As such, we surmise that retail email hijacking has yet to mature to the level of other criminal market segments.

Over the past 20 years, websites have grown increasingly complex and interconnected. In 2016, only a negligible number of sites are dependency free, and over 90% of sites rely on external content. In this paper, we investigate the current state of web dependencies and explore two security challenges associated with the increasing reliance on external services: (1) the expanded attack surface associated with serving unknown, implicitly trusted third-party content, and (2) how the increased set of external dependencies impacts HTTPS adoption. We hope that by shedding light on these issues, we can encourage developers to consider the security risks associated with serving third-party content and prompt service providers to more widely deploy HTTPS.

Industrial control systems have become ubiquitous, enabling the remote, electronic control of physical equipment and sensors. Originally designed to operate on closed networks, the protocols used by these devices have no built-in security. However, despite this, an alarming number of systems are connected to the public Internet and an attacker who finds a device often can cause catastrophic damage to physical infrastructure. We consider two aspects of ICS security in this work: (1) what devices have been inadvertently exposed on the public Internet, and (2) who is searching for vulnerable systems. First, we implement five common SCADA protocols in ZMap and conduct a survey of the public IPv4 address space finding more than 60K publicly accessible systems. Second, we use a large network telescope and high-interaction honeypots to find and profile actors searching for devices. We hope that our findings can both motivate and inform future work on securing industrial control systems.

Fast Internet-wide scanning has opened new avenues for security research, ranging from uncovering widespread vulnerabilities in random number generators to tracking the evolving impact of Heartbleed. However, this technique still requires significant effort: even simple questions, such as, "What models of embedded devices prefer CBC ciphers?", require developing an application scanner, manually identifying and tagging devices, negotiating with network administrators, and responding to abuse complaints. In this paper, we introduce Censys, a public search engine and data processing facility backed by data collected from ongoing Internet-wide scans. Designed to help researchers answer security-related questions, Censys supports full-text searches on protocol banners and querying a wide range of derived fields (e.g., 443.https.cipher). It can identify specific vulnerable devices and networks and generate statistical reports on broad usage patterns and trends. Censys returns these results in sub-second time, dramatically reducing the effort of understanding the hosts that comprise the Internet. We present the search engine architecture and experimentally evaluate its performance. We also explore Censys's applications and show how questions asked in recent studies become simple to answer.

The SMTP protocol is responsible for carrying some of users' most intimate communication, but like other Internet protocols, authentication and confidentiality were added only as an afterthought. In this work, we present the first report on global adoption rates of SMTP security extensions, including: STARTTLS, SPF, DKIM, and DMARC. We present data from two perspectives: SMTP server configurations for the Alexa Top Million domains, and over a year of SMTP connections to and from Gmail. We find that the top mail providers (e.g., Gmail, Yahoo, and Outlook) all proactively encrypt and authenticate messages. However, these best practices have yet to reach widespread adoption in a long tail of over 700,000 SMTP servers, of which only 35% successfully configure encryption, and 1.1% specify a DMARC authentication policy. This security patchwork---paired with SMTP policies that favor failing open to allow gradual deployment---exposes users to attackers who downgrade TLS connections in favor of cleartext and who falsify MX records to reroute messages. We present evidence of such attacks in the wild, highlighting seven countries where more than 20% of inbound Gmail messages arrive in cleartext due to network attackers.