One of the ways in which attackers try to steal sensitive information from corporations is by sending spearphishing emails. This type of emails typically appear to be sent by one of the victim's coworkers, but have instead been crafted by an attacker. A particularly insidious type of spearphishing emails are the ones that do not only claim to come from a trusted party, but were actually sent from that party's legitimate email account that was compromised in the first place. In this paper, we propose a radical change of focus in the techniques used for detecting such malicious emails: instead of looking for particular features that are indicative of attack emails, we look for possible indicators of impersonation of the legitimate owners. We present IdentityMailer, a system that validates the authorship of emails by learning the typical email-sending behavior of users over time, and comparing any subsequent email sent from their accounts against this model. Our experiments on real world e-mail datasets demonstrate that our system can effectively block advanced email attacks sent from genuine email accounts, which traditional protection systems are unable to detect. Moreover, we show that it is resilient to an attacker willing to evade the system. To the best of our knowledge, IdentityMailer is the first system able to identify spearphishing emails that are sent from within an organization, by a skilled attacker having access to a compromised email account.
presented ASCAI @cite_42 , a system that detects if an email author has likely been forged. ASCAI looks at the most common n-grams in a user's emails, and flag as anomalous emails that contain words that the user rarely uses. Unlike , ASCAI looks for any word, instead of focusing on writeprint features (such as functional words). For this reason, this system would fail in detecting spearphishing emails whose content is about the same topics that the user typically discusses, but that have been authored by a different person. , on the other hand, has been designed to detect this type of stealthy spearphishing emails, and is therefore effective in blocking them.
@cite_42
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Phishing is a semantic attack that takes advantage of the naivety of the human behind electronic systems (e.g. e-banking). Educating end-users can minimize the impact of phishing attacks, however it remains relatively expensive and time consuming. Thus, many software-based solutions, such as classifiers, are being proposed by researchers. However, no software solutions have been proposed to minimize the impact of spear phishing attacks, which are the targeted form of phishing, and have a higher success rate than generic bulk phishing attacks. In this paper, we describe a novel framework to mitigate spear phishing attacks via the use of document authorship techniques — Anti-Spear phishing Content-based Authorship Identification (ASCAI). ASCAI informs the user of possible mismatches between the writing styles of a received email body and of trusted authors by studying the email body itself (i.e. the writeprint), as opposed to traditional user ID-based authentication techniques which can be spoofed or abused. As a proof of concept, we implemented the proposed framework using Source Code Author Profiles (SCAP), and the evaluation results are presented. E-mail has become the most popular Internet application and with its rise in use has come an inevitable increase in the use of e-mail for criminal purposes. It is possible for an e-mail message to be sent anonymously or through spoofed servers. Computer forensics analysts need a tool that can be used to identify the author of such e-mail messages. This thesis describes the development of such a tool using techniques from the fields of stylometry and machine learning. An author's style can be reduced to a pattern by making measurements of various stylometric features from the text. E-mail messages also contain macro-structural features that can be measured. These features together can be used with the Support Vector Machine learning algorithm to classify or attribute authorship of e-mail messages to an author providing a suitable sample of messages is available for comparison. In an investigation, the set of authors may need to be reduced from an initial large list of possible suspects. This research has trialled authorship characterisation based on sociolinguistic cohorts, such as gender and language background, as a technique for profiling the anonymous message so that the suspect list can be reduced. The goal of keyword spotting is to detect the presence of specific spoken words in unconstrained speech. The majority of keyword spotting systems are based on generative hidden Markov models and lack discriminative capabilities. However, discriminative keyword spotting systems are currently based on frame-level posterior probabilities of sub-word units. This paper presents a discriminative keyword spotting system based on recurrent neural networks only, that uses information from long time spans to estimate word-level posterior probabilities. In a keyword spotting task on a large database of unconstrained speech the system achieved a keyword spotting accuracy of 84.5 We describe the use of machine learning and data mining to detect and classify malicious executables as they appear in the wild. We gathered 1,971 benign and 1,651 malicious executables and encoded each as a training example using n-grams of byte codes as features. Such processing resulted in more than 255 million distinct n-grams. After selecting the most relevant n-grams for prediction, we evaluated a variety of inductive methods, including naive Bayes, decision trees, support vector machines, and boosting. Ultimately, boosted decision trees outperformed other methods with an area under the ROC curve of 0.996. Results suggest that our methodology will scale to larger collections of executables. We also evaluated how well the methods classified executables based on the function of their payload, such as opening a backdoor and mass-mailing. Areas under the ROC curve for detecting payload function were in the neighborhood of 0.9, which were smaller than those for the detection task. However, we attribute this drop in performance to fewer training examples and to the challenge of obtaining properly labeled examples, rather than to a failing of the methodology or to some inherent difficulty of the classification task. Finally, we applied detectors to 291 malicious executables discovered after we gathered our original collection, and boosted decision trees achieved a true-positive rate of 0.98 for a desired false-positive rate of 0.05. This result is particularly important, for it suggests that our methodology could be used as the basis for an operational system for detecting previously undiscovered malicious executables.