A recent set of attacks aimed at North Korean defectors and journalists were associated with a highly targeted campaign conducted by an actor that does not appear to be related to any known cybercrime groups, McAfee says.
The attacks used a range of vectors to infect victims with malware, including email, the KakaoTalk chat application (which is popular in South Korea), and social network services such as Facebook. Some of the attacks also employed Google-shortened URLs to spread malware.
McAfee’s research into the incident revealed the use of two versions of the dropper malware, namely applications called “Pray for North Korea” and “BloodAssistant.” Most of the clicks leading to infection originated from South Korea in both cases, McAfee’s security researchers discovered.
The most frequently observed browser and operating system combination for the clicks was Chrome and Windows, with Android coming in second, McAfee notes in a technical report. Furthermore, the investigation revealed that Facebook was used in 12% of infections to send a malicious link to the targets.
The Trojan used in this campaign, which McAfee detects as Android/HiddenApp.BP, is dropped onto the victim’s device via malicious APK files. Although various malicious apps are used for malware delivery, the dropper mechanism is identical, the researchers say.
The dropper first checks whether the device hasn’t been already infected, then tricks the victim into enabling accessibility permissions. The application then displays an overlay to hide the fact that it turns on required settings and downloads and installs the Trojan. The overlay is removed once the installation has been completed.
The Trojan uses cloud services such as Dropox and Yandex as the command and control (C&C) server. Once installed, it uploads device information to the cloud, then downloads a file containing commands and other data to control the infected device. Malicious behavior such as saving SMS messages and contact information is implemented in a separate DEX file.
Variants of the malicious APKs were found on Google Drive, some using different cloud services as C&Cs, while others also dropping a separate call-recording application.
The researchers discovered that the initial malicious APKs were uploaded to Google Drive from a single account, which was also associated with a social network account. The same account is believed to have been used to send shortened URLs to victims.
The group behind the account appears to know the South Korean culture well, yet the account also revealed the use of the North Korean word for “blood type,” instead of the South Korean word. A North Korean IP address was also found in test log files on some Android devices connected to accounts used to spread the malware.
The researchers also discovered a deleted folder named Sun Team, supposedly revealing the name of the actor behind the campaign, which has been supposedly active since 2016.
“This malware campaign is highly targeted, using social network services and KakaoTalk to directly approach targets and implant spyware. We cannot confirm who is behind this campaign, and the possible actor Sun Team is not related to any previously known cybercrime groups. The actors are familiar with South Korea and appear to want to spy on North Korean defectors, and on groups and individuals who help defectors,” McAfee concludes.
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Ionut Arghire is an international correspondent for SecurityWeek.
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