Discretionary Access Control (DAC) is the primary access control mechanism in today’s major operating systems. It is, however, vulnerable to Trojan Horse attacks and attacks exploiting buggy software. We propose to combine the discretionary policy in DAC with the dynamic information flow techniques in MAC, therefore achieving the best of both worlds, that is, the DAC’s easy-to-use discretionary policy specification and MAC’s defense against threats caused by Trojan Horses and buggy programs. We propose the Information Flow Enhanced Discretionary Access Control (IFEDAC) model that implements this design philosophy. We describe our design of IFEDAC, and discuss its relationship with the Usable Mandatory Integrity Protection (UMIP) model proposed earlier by us. In addition, we analyze their security property and their relationships with other protection systems. We also describe our implementations of IFEDAC in Linux and the evaluation results and deployment experiences of the systems.

An operating system relies heavily on its access control mechanisms to defend against local and remote attacks. The complexities of modern access control mechanisms and the scale of possible configurations are often overwhelming to system administrators and software developers. Therefore mis-configurations are very common and the security consequences are serious. Given the popularity and uniqueness of Microsoft Windows systems, it is critical to have a tool to comprehensively examine the access control configurations. However, current studies on Windows access control mechanisms are mostly based on known attack patterns. We propose a tool, WACCA, to systematically analyze the Windows configurations. Given the attacker's initial abilities and goals, WACCA generates an attack graph based on interaction rules. The tool then automatically generates attack patterns from the attack graph. Each attack pattern represents attacks of the same nature. The attack subgraphs and instances are also generated for each pattern. Compared to existing solutions, WACCA is more comprehensive and does not rely on manually defined attack patterns. It also has a unique feature in that it models software vulnerabilities and therefore can find attacks that rely on exploiting these vulnerabilities. We study two attack cases on a Windows Vista host and discuss the analysis results.

Modern operating systems primarily use Discretionary Access Control (DAC) to protect files and other operating system resources. DAC mechanisms are more user-friendly than Mandatory Access Control (MAC) systems, but are vulnerable to attacks that use trojan horses or exploit buggy software. We show that it is possible to have the best of both worlds: DAC's easy-to-use discretionary policy and MAC's defense against trojan horses and buggy programs. This is made possible by a key new insight that DAC has weaknesses not because it uses the discretionary principle, but because existing DAC enforcement mechanisms assume that a single principal is responsible for any request, whereas in reality a request may be influenced by multiple principals; thus these mechanisms cannot correctly identify the true origin(s) of a request and fall prey to trojan horses. We propose to solve this problem by combining DAC's policy specification with new enforcement techniques that use ideas from MAC's information flow tracking. Our model, called Information Flow Enhanced DAC (IFEDAC), significantly strengthens end host security, while preserving to a large degree DAC's ease of use. In this paper, we present the IFEDAC model, analyze its security properties, and discuss our implementation for Linux.

While many role mining algorithms have been proposed in recent years, there lacks a comprehensive study to compare these algorithms. These role mining algorithms have been evaluated when they were proposed, but the evaluations were using different datasets and evaluation criteria. In this paper, we introduce a comprehensive framework for evaluating role mining algorithms. We categorize role mining algorithms into two classes based on their outputs; Class 1 algorithms output a sequence of prioritized roles while Class 2 algorithms output complete RBAC states. We then develop techniques that enable us to compare these algorithms directly. We also introduce a new role mining algorithm and two new ways for algorithmically generating datasets for evaluation. Using synthetic as well as real datasets, we compared nine role mining algorithms. Our results illustrate the strengths and weaknesses of these algorithms.

HTTPS is designed to provide secure web communications over insecure networks. The protocol itself has been rigorously designed and evaluated by assuming the network as an adversary. This paper is motivated by our curiosity about whether such an adversary has been carefully examined when HTTPS is integrated into the browser/web systems. We focus on a specific adversary named “Pretty-Bad-Proxy” (PBP). PBP is a malicious proxy targeting browsers’ rendering modules above the HTTP/HTTPS layer. It attempts to break the end-to-end security guarantees of HTTPS without breaking any cryptographic scheme. We discovered a set of vulnerabilities exploitable by a PBP: in many realistic network environments where attackers can sniff the browser traffic, they can steal sensitive data from an HTTPS server, fake an HTTPS page and impersonate an authenticated user to access an HTTPS server. These vulnerabilities reflect the neglects in the design of modern browsers – they affect multiple major browsers and a large number of websites. We believe that the PBP adversary has not been rigorously examined in the browser/web industry. The vendors of the affected browsers have all confirmed the vulnerabilities reported in this paper. Most of them have patched or planned on patching their browsers. We believe the attack scenarios described in this paper may only be a subset of the vulnerabilities under PBP. Thus further (and more rigorous) evaluations of the HTTPS deployments in browsers appear to be necessary.

Administration of large-scale RBAC systems is a challenging open problem. We propose a principled approach in designing and analyzing administrative models for RBAC. We identify six design requirements for administrative models of RBAC. These design requirements are motivated by three principles for designing security mechanisms: (1) flexibility and scalability, (2) psychological acceptability, and (3) economy of mechanism. We then use these requirements to analyze several approaches to RBAC administration, including ARBAC97 [21, 23, 22], SARBAC [4, 5], and the RBAC system in the Oracle DBMS. Based on these requirements and the lessons learned in analyzing existing approaches, we design UARBAC, a new family of administrative models for RBAC that has significant advantages over existing models.

Existing mandatory access control systems for operating systems are difficult to use. We identify several principles for designing usable access control systems and introduce the usable mandatory integrity protection (UMIP) model that adds usable mandatory access control to operating systems. The UMIP model is designed to preserve system integrity in the face of network-based attacks. The usability goals for UMIP are twofold. First, configuring a UMIP system should not be more difficult than installing and configuring an operating system. Second, existing applications and common usage practices can still be used under UMIP. UMIP has several novel features to achieve these goals. For example, it introduces several concepts for expressing partial trust in programs. Furthermore, it leverages information in the existing discretionary access control mechanism to derive file labels for mandatory integrity protection. We also discuss our implementation of the UMIP model for Linux using the Linux Security Modules framework, and show that it is simple to configure, has low overhead, and effectively defends against a number of network-based attacks.