To date, most work regarding the formal analysis of access control schemes has focused on quantifying and comparing the expressive power of a set of schemes. Although expressive power is important, it is a property that exists in an *absolute* sense, detached from the application context within which an access control scheme will ultimately be deployed. By contrast, we formalize the access control *suitability analysis problem*, which seeks to evaluate the degree to which a set of candidate access control schemes can meet the needs of an application-specific workload. This process involves both reductions to assess whether a scheme is *capable* of implementing a workload (qualitative analysis), as well as cost analysis using ordered measures to quantify the *overheads* of using each candidate scheme to service the workload (quantitative analysis). We formalize the two-facet suitability analysis problem, which formally describes this task. We then develop a mathematical framework for this type of analysis, and evaluate this framework both formally, by quantifying its efficiency and accuracy properties, and practically, by exploring an academic program committee workload.

Parameter tampering attacks are dangerous to a web application whose server fails to replicate the validation of user-supplied data that is performed by the client in web forms. Malicious users who circumvent the client can capitalize on the missing server validation. In this paper, we provide a formal description of parameter tampering vulnerabilities and a high level approach for their detection. We specialize this high level approach to develop complementary detection solutions in two interesting settings: blackbox (only analyze client-side code in web forms) and whitebox (also analyze server-side code that processes submitted web forms). This paper presents interesting challenges encountered in realizing the high level approach for each setting and novel technical contributions that address these challenges. We also contrast utility, difficulties and effectiveness issues in both settings and provide a quantitative comparison of results. Our experiments with real world and open source applications demonstrate that parameter tampering vulnerabilities are prolific (total 47 in 9 applications), and their exploitation can have serious consequences including unauthorized transactions, account hijacking and financial losses. We conclude this paper with a discussion on countermeasures for parameter tampering attacks and present a detailed survey of existing defenses and their suitability.

Parameter tampering attacks are dangerous to a web application whose server performs weaker data sanitization than its client. This paper presents TamperProof, a methodology and tool that offers a novel and efficient mechanism to protect Web applications from parameter tampering attacks. TamperProof is an online defense deployed in a trusted environment between the client and server and requires no access to, or knowledge of, the server side codebase, making it effective for both new and legacy applications. The paper reports on experiments that demonstrate TamperProof's power in efficiently preventing all known parameter tampering vulnerabilities on ten different applications.

Access control schemes come in all shapes and sizes, which makes choosing the right one for a particular application a challenge. Yet today's techniques for comparing access control schemes completely ignore the setting in which the scheme is to be deployed. In this paper, we present a formal framework for comparing access control schemes with respect to a particular application. The analyst's main task is to evaluate an access control scheme in terms of how well it implements a given access control workload (a formalism that we introduce to represent an application's access control needs). One implementation is better than another if it has stronger security guarantees, and in this paper we introduce several such guarantees: correctness, homomorphism, AC-preservation, safety, administration-preservation, and compatibility. The scheme that admits the implementation with the strongest guarantees is deemed the best fit for the application. We demonstrate the use of our framework by evaluating two workloads on ten different access control schemes.

Access control is an area where one size does not fit all. However, previous work in access control has focused solely on expressiveness as an absolute measure. Thus, we discuss and justify the need for a new type of evaluation framework for access control, one that is application-aware. To this end, we apply previous work in access control evaluation, as well as lessons learned from evaluation frameworks used in other domains. We describe the analysis components required by such a framework, the challenges involved in building it, and our preliminary work in realizing this ambitious goal. We then theorize about other areas within the security domain that display a similar absence of such evaluation tools, and consider ways in which we can adapt our framework to analyze these broader types of security workloads.

Parameter tampering attacks are dangerous to a web application whose server fails to replicate the validation of user-supplied data that is performed by the client. Malicious users who circumvent the client can capitalize on the missing server validation. In this paper, we describe WAPTEC, a tool that is designed to automatically identify parameter tampering vulnerabilities and generate exploits by construction to demonstrate those vulnerabilities. WAPTEC involves a new approach to whitebox analysis of the server's code. We tested WAPTEC on six open source applications and found previously unknown vulnerabilities in every single one of them.

Web applications rely heavily on client-side computation to examine and validate form inputs that are supplied by a user (e.g., "credit card expiration date must be valid"). This is typically done for two reasons: to reduce burden on the server and to avoid latencies in communicating with the server. However, when a server fails to replicate the validation performed on the client, it is potentially vulnerable to attack. In this paper, we present a novel approach for automatically detecting potential server-side vulnerabilities of this kind in existing (legacy) web applications through blackbox analysis. We discuss the design and implementation of NoTamper, a tool that realizes this approach. NoTamper has been employed to discover several previously unknown vulnerabilities in a number of open-source web applications and live web sites.