An Empirical Evaluation of Security Indicators in Mobile Web Browsers
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IEEE TRANSACTIONS ON MOBILE COMPUTING, VOL. 14, NO. 5, MAY 2015 889 An Empirical Evaluation of Security Indicators in Mobile Web Browsers Chaitrali Amrutkar, Patrick Traynor, Member, IEEE, and Paul C. van Oorschot, Member, IEEE Abstract—Mobile browsers are increasingly being relied upon to perform security sensitive operations. Like their desktop counterparts, these applications can enable SSL/TLS to provide strong security guarantees for communications over the web. However, the drastic reduction in screen size and the accompanying reorganization of screen real-estate significantly changes the use and consistency of the security indicators and certificate information that alert users of site identity and the presence of strong cryptographic algorithms. In this paper, we perform the first measurement of the state of critical security indicators in mobile browsers. We evaluate ten mobile and two tablet browsers, representing over 90% of the market share, against the recommended guidelines for web user interface to convey security set forth by the World Wide Web Consortium (W3C). While desktop browsers follow the majority of guidelines, our analysis shows that mobile browsers fall significantly short. We also observe notable inconsistencies across mobile browsers when such mechanisms actually are implemented. We show where and how these failures on mobile browsers eliminate clues previously designed for, and still present in, desktop browsers to detect attacks such as phishing and man-in-the-middle. Finally, we offer advice on where current standards are unclear or incomplete. Index Terms—Measurement, mobile security, SSL indicators, web browsers 1INTRODUCTION OBILE browsers provide a rich set of features that and tablet browsers appear to support similar security M often rival their desktop counterparts. From support indicators when compared to desktop browsers, the rea- for Javascript and access to location information to the abil- sons behind the increasing number of attacks on mobile ity for third-party applications to render content through browsers [27], [30] are not immediately clear. WebViews, browsers are beginning to serve as one of the criti- In this paper, we perform the comprehensive empirical cal enablers of modern mobile computing. Such functionality, evaluation of security indicators in mobile web browsers. in combination with the near universal implementation of The goal of this work is not to determine if average users strong cryptographic tools including SSL/TLS, allows users take advantage of such cues, but instead whether security to become increasingly reliant upon mobile devices to enable indicators are applied in a manner that allows expert users sensitive personal, social and financial exchanges. to accurately determine the identity of a website or verify In spite of the availability of SSL/TLS, mobile users the use of strong cryptographic primitives for communi- are regularly becoming the target of malicious behav- cations. We believe that this distinction is critical because ior. A 2011 report indicates that mobile users are three it highlights areas where not even the best trained users times more likely to access phishing websites than desktop will be able to differentiate between malicious and benign users [8]. Security indicators (i.e., certificate information, behavior. Rather than an ad hoc analysis, we base our study lock icons, cipher selection, etc.) in web browsers offer on the recommendations set forward by the W3C for user one of the few methods to detect such attacks. A user interface security [31] as a proxy for best practices. In par- can view different security indicators and related certifi- ticular, we measure which browsers strictly conform to the cate information presented by the browser to offer signals absolute requirements (“MUST” clauses) and prohibitions or clues about the credibility of a website. Although mobile (“MUST NOT” clauses). We perform our analysis across ten mobile and two tablet browsers, representing greater than 90% of the mobile market share [4], and then compare our results against the five most popular desktop browsers. Our • C. Amrutkar can be reached at E-mail: [email protected]. experiments demonstrate that while the majority of desktop • P. Traynor is with the Southeastern Security for Enterprise and browsers largely meet the W3C recommendations, all mobile Infrastructure Center, University of Florida, Gainesville, FL 32611 USA. E-mail: [email protected]fl.edu. browsers fail to meet many of the guidelines. Additionally, • Paul C. van Oorschot is with the School of Computer Science, Carleton we observe that mobile browsers exhibit tremendous incon- University, Ottawa, ON K1S 5B6, Canada. sistency in the presentation and availability of such indicators E-mail: [email protected]. in contrast to traditional desktop browsers. Manuscript received 25 Sep. 2012; revised 24 Mar. 2013; accepted 12 Apr. Our main contribution is a comprehensive and sys- 2013. Date of publication 15 July 2013; date of current version 30 Mar. 2015. tematic evaluation and comparison of security indicators For information on obtaining reprints of this article, please send e-mail to: [email protected], and reference the Digital Object Identifier below. and security information for mobile and tablet browsers, Digital Object Identifier 10.1109/TMC.2013.90 to our knowledge the first such analysis undertaken. 1536-1233 c 2013 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. 890 IEEE TRANSACTIONS ON MOBILE COMPUTING, VOL. 14, NO. 5, MAY 2015 The main findings of our experiments are that all popular Trust anchor: A trust anchor represents an authoritative mobile and tablet browsers fail to meet, in numerous entity represented by a public key and associated data. instances, the recommendations in the W3C guidelines for The public key is used to verify digital signatures and the user interface of security information, whereas in com- associated data is used to constrain the types of informa- parison desktop browsers largely follow the guidelines. tion for which the trust anchor is authoritative. Relying Our findings of tremendous inconsistency of user interfaces parties (web browsers) use trust anchors to determine if across mobile browsers, and between mobile and desktop digitally signed information objects are valid by verifying browsers, are also expected to be of considerable inter- digital signatures using the trust anchor’s public key and est. Among other contributions, we outline possible attacks by enforcing the constraints expressed in the associated cer- on mobile browsers, such as phishing and undetectable tificate data. Our interpretation is that a trust anchor refers man-in-the-middle, enabled by failure to properly follow to a certificate authority (CA). these guidelines; and we highlight missing security indi- Root: A root is a trust anchor that is any certificate author- cators, e.g., extended validation (EV) SSL indicators [17], ity (CA). [23], [33]. These are intended to convey an augmented assurance process, however we find most mobile browsers Trusted root: A trusted root is a CA whose public key is a fail to implement EV-SSL indicators visible to users, and priori trusted by the browser and may certify other keys. their absence along with that of any distinguishing browser Certificates: Public key certificates are widely used to behavior, precludes EV-SSL certificates from providing rely- provide keying material and convey a website’s identity ing parties any benefits beyond non-EV SSL certificates. information to the user. The W3C defines four types of cer- The remainder of our paper is organized as follows: tificates. We provide our interpretation for the definitions Section 2 provides definitions and explains the mandatory of certificate types in the W3C document where they are elements of the W3C guidelines; Section 3 provides the ambiguous. For additional information regarding the com- primary results of our evaluation; Section 4 discusses sec- mercial practice of issuing and managing SSL certificates, ondary observations; Section 5 presents ways in that a user please refer to the requirements defined by the CA/Browser can be mislead about the identity of a website or the use forum [18]. of encryption and attacks that are enabled by this confu- sion; Section 6 presents an overview of related research; and • Validated certificate: This is a public key certificate that Section 7 offers a discussion of our findings and concluding has been verified by chaining up to a trusted root. remarks. Our interpretation is that a standard SSL certificate signed by a CA trusted by a browser refers to a validated certificate. 2BACKGROUND:W3CRECOMMENDATIONS • Augmented assurance certificate: The certificate chain The World Wide Web Consortium (W3C) has defined user for such a certificate MUST be validated up to a interface guidelines [31] for the presentation and commu- trusted root that is recognized as augmented assur- nication of web security context information to end-users ance qualified by the user agent (user’s browser). of both desktop and mobile browsers. For context in later We interpret an EV-SSL certificate as an augmented sections, we first define the terminology and then provide a assurance certificate that is validated by the browser. brief explanation of the W3C guidelines referenced within • Self-signed certificate and untrusted root certificate: A this paper. self-signed certificate is a certificate that is signed by its own creator and is not a priori trusted by a browser. Our interpretation of an untrusted root cer- 2.1 Definitions tificate is that it refers to a certificate holding the User interface elements: User interface elements in public key of a CA, that is signed by a CA not a browsers are divided in two categories [31]: priori trusted by the user’s browser. • Primary User Interface: the portions of a user interface • Interactively accepted trust anchors or certificates: This that are available to users without being solicited by refers to either a CA or a website’s public key that a user interaction.