SYSTEMATIC POLICY ANALYSIS AND MANAGEMENT

Determining whether a given policy meets a site’s high-level security goals has been a challenging task, due to the low-level nature and complexity of the policy language, various security requirements and the multiple policy violation patterns. In this dissertation, we outline a systematic policy analysis and management approach that enables system administrators to easily identify and resolve various policy violations. Our approach incorporates a domain-based isolation model to address the security requirements and visualization mechanisms to provide the policy administrator with intuitive cognitive sense about the policy analysis and policy violations. Based on the domain-based isolation model and the policy visualization mechanisms, we develop a visualization-based policy analysis and management framework. We also describe our implementation of a visualization-based policy analysis and management tool that provides the functionalities discussed in our framework. In addition, a user study is performed and the result is included as part of our evaluation efforts for the prototype system. One important application of our policy analysis and management is to support remote attestation. Remote attestation is an important mechanism to provide the trustworthiness proof of a computing system by verifying its integrity. In our work, we propose a remote attestation framework, called Dynamic Remote Attestation Framework and Tactics (DR@FT), for efficiently attesting a target system based on our extended visualization-based policy analysis and management approach. In addition, we adopt the proposed visualization-based policy violation expression to represent integrity violations with a ranked violation graph, which supports intuitive reasoning of attestation results. We also describe our experiments and performance evaluation

Identifying Native Applications with High Assurance

The work described in this paper investigates the problem of identifying and deterring stealthy malicious processes on a host. We point out the lack of strong application iden- tication in main stream operating systems. We solve the application identication problem by proposing a novel iden- tication model in which user-level applications are required to present identication proofs at run time to be authenti- cated by the kernel using an embedded secret key. The se- cret key of an application is registered with a trusted kernel using a key registrar and is used to uniquely authenticate and authorize the application. We present a protocol for secure authentication of applications. Additionally, we de- velop a system call monitoring architecture that uses our model to verify the identity of applications when making critical system calls. Our system call monitoring can be integrated with existing policy specication frameworks to enforce application-level access rights. We implement and evaluate a prototype of our monitoring architecture in Linux as device drivers with nearly no modication of the ker- nel. The results from our extensive performance evaluation shows that our prototype incurs low overhead, indicating the feasibility of our model

A FIREWALL MODEL OF FILE SYSTEM SECURITY

File system security is fundamental to the security of UNIX and Linux systems since in these systems almost everything is in the form of a file. To protect the system files and other sensitive user files from unauthorized accesses, certain security schemes are chosen and used by different organizations in their computer systems. A file system security model provides a formal description of a protection system. Each security model is associated with specified security policies which focus on one or more of the security principles: confidentiality, integrity and availability. The security policy is not only about “who” can access an object, but also about “how” a subject can access an object. To enforce the security policies, each access request is checked against the specified policies to decide whether it is allowed or rejected. The current protection schemes in UNIX/Linux systems focus on the access control. Besides the basic access control scheme of the system itself, which includes permission bits, setuid and seteuid mechanism and the root, there are other protection models, such as Capabilities, Domain Type Enforcement (DTE) and Role-Based Access Control (RBAC), supported and used in certain organizations. These models protect the confidentiality of the data directly. The integrity of the data is protected indirectly by only allowing trusted users to operate on the objects. The access control decisions of these models depend on either the identity of the user or the attributes of the process the user can execute, and the attributes of the objects. Adoption of these sophisticated models has been slow; this is likely due to the enormous complexity of specifying controls over a large file system and the need for system administrators to learn a new paradigm for file protection. We propose a new security model: file system firewall. It is an adoption of the familiar network firewall protection model, used to control the data that flows between networked computers, toward file system protection. This model can support decisions of access control based on any system generated attributes about the access requests, e.g., time of day. The access control decisions are not on one entity, such as the account in traditional discretionary access control or the domain name in DTE. In file system firewall, the access decisions are made upon situations on multiple entities. A situation is programmable with predicates on the attributes of subject, object and the system. File system firewall specifies the appropriate actions on these situations. We implemented the prototype of file system firewall on SUSE Linux. Preliminary results of performance tests on the prototype indicate that the runtime overhead is acceptable. We compared file system firewall with TE in SELinux to show that firewall model can accommodate many other access control models. Finally, we show the ease of use of firewall model. When firewall system is restricted to specified part of the system, all the other resources are not affected. This enables a relatively smooth adoption. This fact and that it is a familiar model to system administrators will facilitate adoption and correct use. The user study we conducted on traditional UNIX access control, SELinux and file system firewall confirmed that. The beginner users found it easier to use and faster to learn then traditional UNIX access control scheme and SELinux

Practical assessment of Biba integrity for TCG-enabled platforms

Checking the integrity of an application is necessary to determine if the latter will behave as expected. The method defined by the Trusted Computing Group consists in evaluating the fingerprints of the platform hardware and software components required for the proper functioning of the application to be assessed. However, this only ensures that a process was working correctly at load-time but not for its whole life-cycle. Policy-Reduced Integrity Measurement Architecture (PRIMA) addresses this problem by enforcing a security policy that denies information flows from potentially malicious processes to an application target of the evaluation and its dependencies (requirement introduced by CW-Lite, an evolution of the Biba integrity model). Given the difficulty of deploying PRIMA (as platform administrators have to tune their security policies to satisfy the CW-Lite requirements) we propose in this paper Enhanced IMA, an extended version of the Integrity Measurement Architecture (IMA) that, unlike PRIMA, works almost out of the box and just reports information flows instead of enforcing them. In addition, we introduce a model to evaluate the information reported by Enhanced IMA with existing technique

Additional kernel observer: privilege escalation attack prevention mechanism focusing on system call privilege changes

Cyberattacks, especially attacks that exploit operating system vulnerabilities, have been increasing in recent years. In particular, if administrator privileges are acquired by an attacker through a privilege escalation attack, the attacker can operate the entire system and cause serious damage. In this paper, we propose an additional kernel observer (AKO) that prevents privilege escalation attacks that exploit operating system vulnerabilities. We focus on the fact that a process privilege can be changed only by specific system calls. AKO monitors privilege information changes during system call processing. If AKO detects a privilege change after system call processing, whereby the invoked system call does not originally change the process privilege, AKO regards the change as a privilege escalation attack and applies countermeasures against it. AKO can therefore prevent privilege escalation attacks. Introducing the proposed method in advance can prevent this type of attack by changing any process privilege that was not originally changed in a system call, regardless of the vulnerability type. In this paper, we describe the design and implementation of AKO for Linux x86 64-bit. Moreover, we show that AKO can be expanded to prevent the falsification of various data in the kernel space. Then, we present an expansion example that prevents the invalidation of Security-Enhanced Linux. Finally, our evaluation results show that AKO is effective against privilege escalation attacks, while maintaining low overhead

An Historical Analysis of the SEAndroid Policy Evolution

Android adopted SELinux's mandatory access control (MAC) mechanisms in 2013. Since then, billions of Android devices have benefited from mandatory access control security policies. These policies are expressed in a variety of rules, maintained by Google and extended by Android OEMs. Over the years, the rules have grown to be quite complex, making it challenging to properly understand or configure these policies. In this paper, we perform a measurement study on the SEAndroid repository to understand the evolution of these policies. We propose a new metric to measure the complexity of the policy by expanding policy rules, with their abstraction features such as macros and groups, into primitive "boxes", which we then use to show that the complexity of the SEAndroid policies has been growing exponentially over time. By analyzing the Git commits, snapshot by snapshot, we are also able to analyze the "age" of policy rules, the trend of changes, and the contributor composition. We also look at hallmark events in Android's history, such as the "Stagefright" vulnerability in Android's media facilities, pointing out how these events led to changes in the MAC policies. The growing complexity of Android's mandatory policies suggests that we will eventually hit the limits of our ability to understand these policies, requiring new tools and techniques.Comment: 16 pages, 11 figures, published in ACSAC '1