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Researchers Discover New Obfuscation-As-a-Service Platform

Researchers detail how a Android APK obfuscation service automates detection evasion for highly malicious apps.

A new obfuscation-as-a-service platform detailed by researchers today during the Botconf 2020 virtual conference offers yet another proof point of how robust the cybercriminal economy is at filling market needs for black hats. In this case, enterprising hackers developed a fully automated service platform for protecting mobile malware Android Packet Kits (APKs) from antivirus detection. Offered on a one-off basis or for a recurring monthly subscription, the service was available to mobile malware authors both in English and Russian for at least six months of 2020, potentially longer.

The service was found and examined by a collaborative team from three organizations: Masarah Paquet-Clouston from GoSecure, Vit Sembera from Trend Micro, and Maria Jose Erquiaga and Sebastian Garcia from the Stratosphere Laboratory. They initially got wind of the service — which they've chosen not to name to avoid tipping off the service operators — when they were analyzing activity surrounding the spread of the Geost Android banking Trojan botnet. They uncovered leaked chat logs between Geost botnet operators referring to an obfuscation service and started poking around to discover what was being discussed.

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In their research quest they found a service that provided obfuscation for $20 per APK or $100 for 10 APKs. Alternatively, the provider also offered 30-day unlimited access for $850. Looking further into the service offerings and how it worked, they found over 3,000 APKs files submitted in VirusTotal that appeared to have been obfuscated by the service in 2020. 

Digging into threat intelligence tools by searching with similar slang as the Geost botnet operators used to refer to the service, the researchers found a number of other extant obfuscation-as-a-service competitors operating on Dark Web forums in 2020. This one was unique compared with the other six found in these searches, according to Paquet-Clouston.  

"None of these competitors offered a platform with an API, and all of them said that purchases happen via private message on Jabber or telegram," she said during the presentation, explaining they were all more expensive than the platform they examined. "So our hypothesis is that these competitors are probably doing manual obfuscation, thus the higher prices. The one that we investigated was offering an API and automatic obfuscation, which could have been a competitive edge in the market."

In terms of efficiency of actually evading detection, Paquet-Clouston said the service was "medium quality" and in less malicious applications would actually result in a higher likelihood of detection after being applied to the APK. As a result, the customers of this service are primarily authors of highly malicious apps, for which the obfuscation would be most effective.  

The good news for defenders is that while attackers went to great lengths to automate the service, that process of automation "makes it easier to fingerprint the obfuscation," Paquet-Clouston stated in a post.

For security researchers seeking to dig further into the technical details of the service, Paquet-Clouston has provided hashes related to the obfuscation on her GitHub page.

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