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I hereby declare that I am the sole author of this thesis, that I have exhaustively specified all sources and resources used, and that parts of this thesis-including tables, maps and figures-if taken from other works or from the Internet, whether copied literally or by sense, all have been marked as replications including a citation of the source. Hiermit erkläre ich, dass ich diese Arbeit selbständig verfasst habe, dass ich die verwendeten Quellen und Hilfsmittel vollständig angegeben habe und dass ich die Stellen der Arbeiteinschließlich Tabellen, Karten und Abbildungen-, die anderen Werken oder dem Internet im Wortlaut oder dem Sinn nach entnommen sind, auf jeden Fall unter Angabe der Quelle als Entlehnung kenntlich gemacht habe.

Malicious web pages that use drive-by download attacks or social engineering techniques to install unwanted software on a user's computer have become the main avenue for the propagation of malicious code. To search for malicious web pages, the first step is typically to use a crawler to collect URLs that are live on the Internet. Then, fast prefiltering techniques are employed to reduce the amount of pages that need to be examined by more precise, but slower, analysis tools (such as honeyclients). While effective, these techniques require a substantial amount of resources. A key reason is that the crawler encounters many pages on the web that are benign, that is, the "toxicity" of the stream of URLs being analyzed is low.In this paper, we present EVILSEED, an approach to search the web more efficiently for pages that are likely malicious. EVILSEED starts from an initial seed of known, malicious web pages. Using this seed, our system automatically generates search engines queries to identify other malicious pages that are similar or related to the ones in the initial seed. By doing so, EVILSEED leverages the crawling infrastructure of search engines to retrieve URLs that are much more likely to be malicious than a random page on the web. In other words EVILSEED increases the "toxicity" of the input URL stream. Also, we envision that the features that EVILSEED presents could be directly applied by search engines in their prefilters. We have implemented our approach, and we evaluated it on a large-scale dataset. The results show that EVILSEED is able to identify malicious web pages more efficiently when compared to crawler-based approaches.

Abstract-To handle the growing flood of malware, security vendors and analysts rely on tools that automatically identify and analyze malicious code. Current systems for automated malware analysis typically follow a dynamic approach, executing an unknown program in a controlled environment (sandbox) and recording its runtime behavior. Since dynamic analysis platforms directly run malicious code, they are resilient to popular malware defense techniques such as packing and code obfuscation. Unfortunately, in many cases, only a small subset of all possible malicious behaviors is observed within the short time frame that a malware sample is executed. To mitigate this issue, previous work introduced techniques such as multipath or forced execution to increase the coverage of dynamic malware analysis. Unfortunately, using these techniques is potentially expensive, as the number of paths that require analysis can grow exponentially.In this paper, we propose REANIMATOR, a novel solution to determine the capabilities (malicious functionality) of malware programs. Our solution is based on the insight that we can leverage behavior observed while dynamically executing a specific malware sample to identify similar functionality in other programs. More precisely, when we observe malicious actions during dynamic analysis, we automatically extract and model the parts of the malware binary that are responsible for this behavior. We then leverage these models to check whether similar code is present in other samples. This allows us to statically identify dormant functionality (functionality that is not observed during dynamic analysis) in malicious programs. We evaluate our approach on thousands of realworld malware samples, and we show that our system is successful in identifying additional, malicious functionality. As a result, our approach can significantly improve the coverage of malware analysis results.

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