Luyi Xing

Unauthorized origin crossing on mobile platforms: threats and mitigation

With the progress in mobile computing, web services are increasingly delivered to their users through mobile apps, instead of web browsers. However, unlike the browser, which enforces origin-based security policies to mediate the interactions between the web content from different sources, todays mobile OSes do not have a comparable security mechanism to control the cross-origin communications between apps, as well as those between an app and the web. As a result, a mobile users sensitive web resources could be exposed to the harms from a malicious origin. In this paper, we report the first systematic study on this mobile cross-origin risk. Our study inspects the main cross-origin channels on Android and iOS, including intent, scheme and web-accessing utility classes, and further analyzes the ways popular web services (e.g., Facebook, Dropbox, etc.) and their apps utilize those channels to serve other apps. The research shows that lack of origin-based protection opens the door to a wide spectrum of cross-origin attacks. These attacks are unique to mobile platforms, and their consequences are serious: for example, using carefully designed techniques for mobile cross-site scripting and request forgery, an unauthorized party can obtain a mobile users Facebook/Dropbox authentication credentials and record her text input. We report our findings to related software vendors, who all acknowledged their importance. To address this threat, we designed an origin-based protection mechanism, called Morbs, for mobile OSes. Morbs labels every message with its origin information, lets developers easily specify security policies, and enforce the policies on the mobile channels based on origins. Our evaluation demonstrates the effectiveness of our new technique in defeating unauthorized origin crossing, its efficiency and the convenience for the developers to use such protection.

Upgrading Your Android, Elevating My Malware: Privilege Escalation through Mobile OS Updating

Android is a fast evolving system, with new updates coming out one after another. These updates often completely overhaul a running system, replacing and adding tens of thousands of files across Androids complex architecture, in the presence of critical user data and applications (apps for short). To avoid accidental damages to such data and existing apps, the upgrade process involves complicated program logic, whose security implications, however, are less known. In this paper, we report the first systematic study on the Android updating mechanism, focusing on its Package Management Service (PMS). Our research brought to light a new type of security-critical vulnerabilities, called Pileup flaws, through which a malicious app can strategically declare a set of privileges and attributes on a low-version operating system (OS) and wait until it is upgraded to escalate its privileges on the new system. Specifically, we found that by exploiting the Pileup vulnerabilities, the app can not only acquire a set of newly added system and signature permissions but also determine their settings (e.g., protection levels), and it can further substitute for new system apps, contaminate their data (e.g., cache, cookies of Android default browser) to steal sensitive user information or change security configurations, and prevent installation of critical system services. We systematically analyzed the source code of PMS using a program verification tool and confirmed the presence of those security flaws on all Android official versions and over 3000 customized versions. Our research also identified hundreds of exploit opportunities the adversary can leverage over thousands of devices across different device manufacturers, carriers and countries. To mitigate this threat without endangering user data and apps during an upgrade, we also developed a new detection service, called SecUP, which deploys a scanner on the users device to capture the malicious apps designed to exploit Pileup vulnerabilities, based upon the vulnerability-related information automatically collected from newly released Android OS images.

Seeking Nonsense, Looking for Trouble: Efficient Promotional-Infection Detection through Semantic Inconsistency Search

Promotional infection is an attack in which the adversary exploits a websites weakness to inject illicit advertising content. Detection of such an infection is challenging due to its similarity to legitimate advertising activities. An interesting observation we make in our research is that such an attack almost always incurs a great semantic gap between the infected domain (e.g., a university site) and the content it promotes (e.g., selling cheap viagra). Exploiting this gap, we developed a semantic-based technique, called Semantic Inconsistency Search (SEISE), for efficient and accurate detection of the promotional injections on sponsored top-level domains (sTLD) with explicit semantic meanings. Our approach utilizes Natural Language Processing (NLP) to identify the bad terms (those related to illicit activities like fake drug selling, etc.) most irrelevant to an sTLDs semantics. These terms, which we call irrelevant bad terms (IBTs), are used to query search engines under the sTLD for suspicious domains. Through a semantic analysis on the results page returned by the search engines, SEISE is able to detect those truly infected sites and automatically collect new IBTs from the titles/URLs/snippets of their search result items for finding new infections. Running on 403 sTLDs with an initial 30 seed IBTs, SEISE analyzed 100K fully qualified domain names (FQDN), and along the way automatically gathered nearly 600 IBTs. In the end, our approach detected 11K infected FQDN with a false detection rate of 1.5% and over 90% coverage. Our study shows that by effective detection of infected sTLDs, the bar to promotion infections can be substantially raised, since other non-sTLD vulnerable domains typically have much lower Alexa ranks and are therefore much less attractive for underground advertising. Our findings further bring to light the stunning impacts of such promotional attacks, which compromise FQDNs under 3% of .edu, .gov domains and over one thousand gov.cn domains, including those of leading universities such as stanford.edu, mit.edu, princeton.edu, havard.edu and government institutes such as nsf.gov and nih.gov. We further demonstrate the potential to extend our current technique to protect generic domains such as .com and .org.