Dave Tian

Defending Against Malicious USB Firmware with GoodUSB

USB attacks are becoming more sophisticated. Rather than using USB devices solely as a delivery mechanism for host-side exploits, attackers are targeting the USB stack itself, embedding malicious code in device firmware to covertly request additional USB interfaces, providing unacknowledged and malicious functionality that lies outside the apparent purpose of the device. This allows for attacks such as BadUSB, where a USB storage device with malicious firmware is capable of covertly acting as a keyboard as well, allowing it to inject malicious scripts into the host machine. We observe that the root cause of such attacks is that the USB Stack exposes a set of unrestricted device privileges and note that the most reliable information about a devices capabilities comes from the end users expectation of the devices functionality. We design and implement GoodUSB, a mediation architecture for the Linux USB Stack. We defend against BadUSB attacks by enforcing permissions based on user expectations of device functionality. GoodUSB includes a security image component to simplify use, and a honeypot mechanism for observing suspicious USB activities. GoodUSB introduces only 5.2% performance overhead compared to the unmodified Linux USB subsystem. It is an important step forward in defending against USB attacks and towards allowing the safe deployment of USB devices in the enterprise.

Securing SSL Certificate Verification through Dynamic Linking

Recent discoveries of widespread vulnerabilities in the SSL/TLS protocol stack, particular with regard to the verification of server certificates, has left the security of the Internets communications in doubt. Newly proposed SSL trust enhancements address many of these vulnerabilities, but are slow to be deployed and do not solve the problem of securing existing software. In this work, we provide new mechanisms that offer immediate solutions to addressing vulnerabilities in legacy code. We introduce CertShim, a lightweight retrofit to SSL implementations that protects against SSL vulnerabilities, including those surveyed by Georgiev et. al., in a manner that is transparent to the application. We demonstrate CertShims extensibility by adapting it to work with Convergence, DANE, and Client-Based Key Pinning. CertShim imposes just 20 ms overhead for an SSL verification call, and hooks the SSL dependencies of 94% of Ubuntus most popular packages with no changes necessary to existing applications. This work significantly increases system-wide security of SSL communications in non-browser software, while simultaneously reducing the barriers to evaluating and adopting the myriad alternative proposals to the certificate authority system.

More Guidelines Than Rules: CSRF Vulnerabilities from Noncompliant OAuth 2.0 Implementations

OAuth 2.0 provides an open framework for the authorization of users across the web. While the standard enumerates mandatory security protections for a variety of attacks, many embodiments of this standard allow these protections to be optionally implemented. In this paper, we analyze the extent to which one particularly dangerous vulnerability, Cross Site Request Forgery, exists in real-world deployments. We crawl the Alexa Top 10,000 domains, and conservatively identify that 25i?ź% of websites using OAuth appear vulnerable to CSRF attacks. We then perform an in-depth analysis of four high-profile case studies, which reveal not only weaknesses in sample code provided in SDKs, but also inconsistent implementation of protections among services provided by the same company. From these data points, we argue that protection against known and sometimes subtle security vulnerabilities can not simply be thrust upon developers as an option, but instead must be strongly enforced by Identity Providers before allowing web applications to connect.

Sending Out an SMS: Characterizing the Security of the SMS Ecosystem with Public Gateways

Text messages sent via the Short Message Service (SMS) have revolutionized interpersonal communication. Recent years have also seen this service become a critical component of the security infrastructure, assisting with tasks including identity verification and second-factor authentication. At the same time, this messaging infrastructure has become dramatically more open and connected to public networks than ever before. However, the implications of this openness, the security practices of benign services, and the malicious misuse of this ecosystem are not well understood. In this paper, we provide the first longitudinal study to answer these questions, analyzing nearly 400,000 text messages sent to public online SMS gateways over the course of 14 months. From this data, we are able to identify not only a range of services sending extremely sensitive plaintext data and implementing low entropy solutions for one-use codes, but also offer insights into the prevalence of SMS spam and behaviors indicating that public gateways are primarily used for evading account creation policies that require verified phone numbers. This latter finding has significant implications for research combatting phone-verified account fraud and demonstrates that such evasion will continue to be difficult to detect and prevent.

ProvUSB: Block-level Provenance-Based Data Protection for USB Storage Devices

Defenders of enterprise networks have a critical need to quickly identify the root causes of malware and data leakage. Increasingly, USB storage devices are the media of choice for data exfiltration, malware propagation, and even cyber-warfare. We observe that a critical aspect of explaining and preventing such attacks is understanding the provenance of data (i.e., the lineage of data from its creation to current state) on USB devices as a means of ensuring their safe usage. Unfortunately, provenance tracking is not offered by even sophisticated modern devices. This work presents ProvUSB, an architecture for fine-grained provenance collection and tracking on smart USB devices. ProvUSB maintains data provenance by recording reads and writes at the block layer and reliably identifying hosts editing those blocks through attestation over the USB channel. Our evaluation finds that ProvUSB imposes a one-time 850 ms overhead during USB enumeration, but approaches nearly-bare-metal runtime performance (90% of throughput) on larger files during normal execution, and less than 0.1% storage overhead for provenance in real-world workloads. ProvUSB thus provides essential new techniques in the defense of computer systems and USB storage devices.

CPAC: securing critical infrastructure with cyber-physical access control

Critical infrastructure such as the power grid has become increasingly complex. The addition of computing elements to traditional physical components increases complexity and hampers insight into how elements in the system interact with each other. The result is an infrastructure where operational mistakes, some of which cannot be distinguished from attacks, are more difficult to prevent and have greater potential impact, such as leaking sensitive information to the operator or attacker. In this paper, we present CPAC, a cyber-physical access control solution to manage complexity and mitigate threats in cyber-physical environments, with a focus on the electrical smart grid. CPAC uses information flow analysis based on mathematical models of the physical grid to generate policies enforced through verifiable logic. At the device side, CPAC combines symbolic execution with lightweight dynamic execution monitoring to allow non-intrusive taint analysis on programmable logic controllers in realtime. These components work together to provide a realtime view of all system elements, and allow for more robust and finer-grained protections than any previous solution to securing the grid. We implement a prototype of CPAC using Bachmann PLCs and evaluate several real-world incidents that demonstrate its scalability and effectiveness. The policy checking for a nation-wide grid is less than 150 ms, faster than existing solutions. We additionally show that CPAC can analyze potential component failures for arbitrary component failures, far beyond the capabilities of currently deployed systems. CPAC thus provides a solution to secure the modern smart grid from operator mistakes or insider attacks, maintain operational privacy, and support N - x contingencies.

FirmUSB: Vetting USB Device Firmware using Domain Informed Symbolic Execution

The USB protocol has become ubiquitous, supporting devices from high-powered computing devices to small embedded devices and control systems. USBs greatest feature, its openness and expandability, is also its weakness, and attacks such as BadUSB exploit the unconstrained functionality afforded to these devices as a vector for compromise. Fundamentally, it is virtually impossible to know whether a USB device is benign or malicious. This work introduces FirmUSB, a USB-specific firmware analysis framework that uses domain knowledge of the USB protocol to examine firmware images and determine the activity that they can produce. Embedded USB devices use microcontrollers that have not been well studied by the binary analysis community, and our work demonstrates how lifters into popular intermediate representations for analysis can be built, as well as the challenges of doing so. We develop targeting algorithms and use domain knowledge to speed up these processes by a factor of 7 compared to unconstrained fully symbolic execution. We also successfully find malicious activity in embedded 8051 firmwares without the use of source code. Finally, we provide insights into the challenges of symbolic analysis on embedded architectures and provide guidance on improving tools to better handle this important class of devices.

Taming the Costs of Trustworthy Provenance through Policy Reduction

Provenance is an increasingly important tool for understanding and even actively preventing system intrusion, but the excessive storage burden imposed by automatic provenance collection threatens to undermine its value in practice. This situation is made worse by the fact that the majority of this metadata is unlikely to be of interest to an administrator, instead describing system noise or other background activities that are not germane to the forensic investigation. To date, storing data provenance in perpetuity was a necessary concession in even the most advanced provenance tracking systems in order to ensure the completeness of the provenance record for future analyses. In this work, we overcome this obstacle by proposing a policy-based approach to provenance filtering, leveraging the confinement properties provided by Mandatory Access Control (MAC) systems in order to identify and isolate subdomains of system activity for which to collect provenance. We introduce the notion of minimal completeness for provenance graphs, and design and implement a system that provides this property by exclusively collecting provenance for the trusted computing base of a target application. In evaluation, we discover that, while the efficacy of our approach is domain dependent, storage costs can be reduced by as much as 89% in critical scenarios such as provenance tracking in cloud computing data centers. To the best of our knowledge, this is the first policy-based provenance monitor to appear in the literature.

Detecting SMS Spam in the Age of Legitimate Bulk Messaging

Text messaging is used by more people around the world than any other communications technology. As such, it presents a desirable medium for spammers. While this problem has been studied by many researchers over the years, the recent increase in legitimate bulk traffic (e.g., account verification, 2FA, etc.) has dramatically changed the mix of traffic seen in this space, reducing the effectiveness of previous spam classification efforts. This paper demonstrates the performance degradation of those detectors when used on a large-scale corpus of text messages containing both bulk and spam messages. Against our labeled dataset of text messages collected over 14 months, the precision and recall of past classifiers fall to 23.8% and 61.3% respectively. However, using our classification techniques and labeled clusters, precision and recall rise to 100% and 96.8%. We not only show that our collected dataset helps to correct many of the overtraining errors seen in previous studies, but also present insights into a number of current SMS spam campaigns.

Securing ARP/NDP From the Ground Up

The basis for all IPv4 network communication is the address resolution protocol (ARP), which maps an IP address to a device’s media access control identifier. ARP has long been recognized as vulnerable to spoofing and other attacks, and past proposals to secure the protocol have often involved in modifying the basic protocol. Similarly, neighbor discovery protocol (NDP) is the basis for all IPv6 network communication, yet suffers from the same vulnerabilities as ARP. This paper introduces arpsec, a secure ARP/RARP protocol suite which a) does not require protocol modification, b) enables continual verification of the identity of the target (respondent) machine by introducing an address binding repository derived using a formal logic that bases additions to a host’s ARP cache on a set of operational rules and properties, c) utilizes the trusted platform module (TPM), a commodity component now present in the vast majority of modern computers, to augment the logic-prover-derived assurance when needed, with TPM-facilitated attestations of system state achieved at viably low-processing cost, and d) supports IPv6 NDP (ndpsec) by extension of our previous work. Using commodity TPMs as our attestation base, we show that arpsec incurs an overhead ranging from 7% to 15.4% over the standard Linux ARP implementation, a comparable overhead against the standard Linux NDP implementation, and provides a first step towards a formally secure and trustworthy networking stack for both IPv4 and IPv6.