Researchers Link New Android Backdoor to North Korean Hackers

The recently discovered KevDroid Android backdoor is tied to the North Korean hacking group APT37, Palo Alto Networks researchers say.

Also tracked as Reaper, Group 123, Red Eyes, and ScarCruft, the threat group was observed earlier this year to be using a Flash Player zero-day vulnerability and  has been expanding the scope and sophistication of its campaigns over the past months.

Recently, the group was said to have targeted victims with Android spyware via spear phishing emails. Cisco’s Talos security researchers analyzed the malware, which they called KevDroid, but weren’t able to find a strong connection with the group.

According to Palo Alto Networks, however, KevDroid is indeed part of APT37’s arsenal of mobile tools. Furthermore, the security researchers were able to find a more advanced version of the spyware, as well as Trojanized iterations of legitimate applications that are used as downloaders for the malware.

The Android spyware was initially found to be masquerading as an anti-virus app from Naver, a large search and web portal service provider in South Korea.

One version of the malware, Palo Alto’s Ruchna Nigam discovered, would call home to cgalim[.]com, a domain already associated with the Reaper group’s non-mobile attacks. Artefacts from the original malware variant eventually revealed a more advanced iteration of the malware, the security researcher notes.

The threat actor apparently uses two Trojanized application versions to distribute Android spyware variants. The legitimate applications – Bitcoin Ticker Widget and PyeongChang Winter Games – are distributed through Google Play, but the malicious variants never made it to the official app store.

The two Trojanized applications, which are signed with the same certificate, contact the same URL to fetch payloads, and were observed serving an advanced iteration of the Android spyware. Each of the malicious apps was created to “respectively download and drop one specific variant of Reaper’s Android spyware,” the Nigam says.

Once installed, the apps would display a message asking the user to update them. If the user accepts the update, however, the malicious payload is downloaded instead and saved as AppName.apk. Next, the payload is loaded and the user is asked to confirm the installation.

The spyware can record audio and video, capture screenshots, grab the phone’s file listing, fetch specific files, download a list of commands, get device info, and root the device. Additionally, it can steal voice recordings from incoming and outgoing calls, call logs, SMS history, contact lists, and information on registered accounts on the phone.

Unlike the previously detailed variants of the malware that used an open source library to record calls, the most recent – and more advanced – variant of the malware writes its own call recording library.

“The emergence of a new attack vector, followed by the appearance of new variants disguising themselves as currently relevant applications like the Winter Olympics, indicates expanding operations of the Reaper group that are actively in development,” Nigam concludes.

Related: New KevDroid Android Backdoor Discovered

RelatedNorth Korean Hacking Group APT37 Expands Targets

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Ionut Arghire is an international correspondent for SecurityWeek.

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