Malware & Machine Learning 2

05 April 2017, 16:35, A6-005

Session chair: Robert H. Deng, Singapore Management University, Singapore

The Role of Hosting Providers in Fighting Command and Control Infrastructure of Financial Malware

Samaneh Tajalizadehkhoob, Carlos Ganan, Arman Noroozian, Michel van Eeten

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A variety of botnets are used in attacks on financial services. Banks and security firms invest a lot of effort in detecting and combating malware-assisted takeover of customer accounts. A critical resource of these botnets is their command-and-control (C&C) infrastructure. Attackers rent or compromise servers to operate their C&C infrastructure. Hosting providers routinely take down C&C servers, but the effectiveness of this mitigation strategy depends on understanding how attackers select the hosting providers to host their servers. Do they prefer, for example, providers who are slow or unwilling in taking down C&Cs? In this paper, we analyze 7 years of data on the C&C servers of botnets that have engaged in attacks on financial services. Our aim is to understand whether attackers prefer certain types of providers or whether their C&Cs are randomly distributed across the whole attack surface of the hosting industry. We extract a set of structural properties of providers to capture the attack surface. We model the distribution of C&Cs across providers and show that the mere size of the provider can explain around 71% of the variance in the number of C&Cs per provider, whereas the rule of law in the country only explains around 1%. We further observe that price, time in business, popularity and ratio of vulnerable websites of providers relate significantly with C&C counts. Finally, we find that the speed with which providers take down C&C domains has only a weak relation with C&C occurrence rates, adding only 1% explained variance. This suggests attackers have little to no preference for providers who allow long-lived C&C domains.

Automatically Inferring Malware Signatures for Anti-Virus Assisted Attacks

Christian Wressnegger, Kevin Freeman, Fabian Yamaguchi, Konrad Rieck

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Although anti-virus software has significantly evolved over the last decade, classic signature matching based on byte patterns is still a prevalent concept for identifying security threats. Anti-virus signatures are a simple and fast detection mechanism that can complement more sophisticated analysis strategies. However, if signatures are not designed with care, they can turn from a defensive mechanism into an instrument of attack. In this paper, we present a novel method for automatically deriving signatures from anti-virus software and discuss how the extracted signatures can be used to attack sensible data with the aid of the virus scanner itself. To this end, we study the practicability of our approach using four commercial products and exemplary demonstrate anti-virus assisted attacks in three different scenarios.

PayBreak: Defense Against Cryptographic Ransomware

Eugene Kolodenker, William Koch, Gianluca Stringhini, Manuel Egele

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Similar to criminals in the physical world, cyber-criminals use a variety of illegal and immoral means to achieve monetary gains. Recently, malware known as ransomware started to leverage strong cryptographic primitives to hold victims’ computer files “hostage” until a ransom is paid. Victims, with no way to defend themselves, are often advised to simply pay. Existing defenses against ransomware rely on ad-hoc mitigations that target the incorrect use of cryptography rather than generic live protection. To fill this gap in the defender’s arsenal, we describe the approach, prototype implementation, and evaluation of a novel, automated, and most importantly proactive defense mechanism against ransomware. Our prototype, called PayBreak, effectively combats ransomware, and keeps victims’ files safe. PayBreak is based on the insight that secure file encryption relies on hybrid encryption where symmetric session keys are used on the victim computer. PayBreak observes the use of these keys, holds them in escrow, and thus, can decrypt files that would otherwise only be recoverable by paying the ransom. Our prototype leverages low overhead dynamic hooking techniques and asymmetric encryption to realize the key escrow mechanism which allows victims to restore the files encrypted by ransomware. We evaluated PayBreak for its effectiveness against twenty hugely successful families of real-world ransomware, and demonstrate that our system can restore all files that are encrypted by samples from twelve of these families, including the infamous CryptoLocker, and more recent threats such as Locky and SamSam. Finally, PayBreak performs its protection task at negligible performance overhead for common office workloads and is thus ideally suited as a proactive online protection system.