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Visual CAPTCHAs have been widely used across the Internet to defend against undesirable or malicious bot programs. In this paper, we document how we have broken most such visual schemes provided at Captchaservice.org, a publicly available web service for CAPTCHA generation. These schemes were effectively resistant to attacks conducted using a high-quality Optical Character Recognition program, but...
Wireless sensor nodes lack hardware support for tamper- resistance and are often deployed in unattended environments, thus leaving them vulnerable to capture and compromise by an adversary. In a node replication attack, an adversary uses the credentials of a compromised node to surreptitiously introduce replicas of that node into the network. These replicas are then used to launch a variety of attacks...
Heap and stack buffer overflows are still among the most common attack vectors in intrusion attempts. In this paper, we ask a simple question that is surprisingly difficult to answer: which bytes contributed to the overflow? By careful observation of all scenarios that may occur in overflows, we identified the information that needs to be tracked to pinpoint the offending bytes. There are many reasons...
Instant messaging (IM) has been one of most frequently used malware attack vectors due to its popularity. Distinct from other malware, it is straightforward for IM malware to find and hit the next victim by exploiting the current victim's contact list and playing social engineering tricks. Thus, the spread of IM malware is much harder to detect and suppress through conventional approaches. The previous...
Special purpose trusted computing devices are currently being deployed to offer many services for which the general purpose computing paradigm is unsuitable. The nature of the services offered by many of these devices demand high security and reliability, as well as low cost and low power consumption. Electronic Voting machines is a canonical example of this phenomenon. With electronic voting machines...
With the recent rapid increase in interactive Web applications that employ back-end database services, an SQL injection attack has become one of the most serious security threats. The SQL injection attack allows an attacker to access the underlying database, execute arbitrary commands at intent, and receive a dynamically generated output, such as HTML Web pages. In this paper, we present our technique,...
Various attacks (e.g., SQL injections) may corrupt data items in the database systems, which decreases the integrity level of the database. Intrusion detections systems are becoming more and more sophisticated to detect such attacks. However, more advanced detection techniques require more complicated analyses, e.g, sequential analysis, which incurs detection latency. If we have an intrusion detection...
The Web is an indispensable part of our lives. Every day, millions of users purchase items, transfer money, retrieve information and communicate over the Web. Although the Web is convenient for many users because it provides any time, anywhere access to information and services, at the same time, it has also become a prime target for miscreants who attack unsuspecting Web users with the aim of making...
We have implemented an information flow framework for the Java virtual machine that combines static and dynamic techniques to capture not only explicit flows, but also implicit ones resulting from control flow. Unlike other approaches that freeze policies at time of compilation, our system truly separates policy and enforcement mechanism and thereby permits policy changes even while a program is running...
A format string attack exploits the fact that variadic functions determine the exact number of input arguments based on the format string argument, and compromises the victim application's address space by accessing data areas beyond the original input argument list the caller prepares. This paper describes the design, implementation and evaluation of a Win32 binary transformation tool called Lisbon,...
Understanding security bugs in a vulnerable program is a non-trivial task, even if the target program is known to be vulnerable. Though there exist debugging tools that facilitate the vulnerability analysis and debugging process, human developers still need to manually trace the program execution most of the times. This makes security debugging a difficult and tiresome task even for experienced programmers...
Security-typed languages (STLs) are powerful tools for provably implementing policy in applications. The programmer maps policy onto programs by annotating types with information flow labels, and the STL compiler guarantees that data always obeys its label as it flows within an application. As data flows into or out of an application, however, a runtime system is needed to mediate between the information...
Malicious software (or malware) has become a growing threat as malware writers have learned that signature- based detectors can be easily evaded by "packing" the malicious payload in layers of compression or encryption. State-of-the-art malware detectors have adopted both static and dynamic techniques to recover the pay- load of packed malware, but unfortunately such techniques are highly...
This paper describes the security and network architecture of the Annex system, a family of technologies for secure and pervasive communication and information processing that we have developed at the Australian Government's Defence Science and Technology Organisation. Our security architecture is built on top of a distributed object-capability system, which we believe provides an ideal platform for...
We propose a taxonomy of botnet structures, based on their utility to the botmaster. We propose key metrics to measure their utility for various activities (e.g., spam, ddos). Using these performance metrics, we consider the ability of different response techniques to degrade or disrupt botnets. In particular, our models show that targeted responses are particularly effective against scale free botnets...
Given a large component-based program, it may be very complex to identify an optimal access-control policy, allowing the program to execute with no authorization failures and no violations of the principle of least privilege. This paper presents a novel combination of static and dynamic analysis for automatic determination of precise access-control policies for programs that will be executed on stack-based...
Integrity measurements provide a means by which distributed systems can assess the trustability of potentially compromised remote hosts. However, current measurement techniques simply assert the identity of software, but provide no indication of the ongoing status of the system or its data. As a result, a number of significant vulnerabilities can result if the system is not configured and managed...
Progress in insider-threat detection is currently limited by a lack of realistic, publicly available, real-world data. For reasons of privacy and confidentiality, no one wants to expose their sensitive data to the research community. Data can be sanitized to mitigate privacy and confidentiality concerns, but the mere act of sanitizing the data may introduce artifacts that compromise its utility for...
Kerberos is a well-established authentication system. As new authentication methods arise, incorporating them into Kerberos is desirable. However, extending Kerberos poses challenges due to a lack of source code availability for some implementations and a lengthy standardization process. This paper presents Extensible Pre-Authentication in Kerberos (EPAK), a Kerberos extension that enables many authentication...
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