Cyble analyzes stealthy Android spyware targeting South Koreans, using an Amazon AWS S3 bucket to store exfiltrated data, including SMSs, contacts, and media.

Key Takeaways

• Since June 2024, a new Android Spyware campaign has been identified targeting individuals in South Korea, leveraging an Amazon AWS S3 bucket as its Command and Control (C&C) server.
• The Spyware is capable of exfiltrating sensitive information from an infected device, including SMSs, contact lists, images, and videos.
• The stolen data, stored openly on the S3 bucket, suggests poor operational security, potentially leading to unintended leaks of sensitive information.
• The spyware operates with a simple source code and few key permissions, demonstrating that even simple malware can be highly effective in exfiltrating sensitive data.
• The malware remained undetected by all major antivirus solutions. Four unique samples were identified, exhibiting zero detection rates across all engines.

Overview

Two malicious URLs distributing the spyware have been identified:

• hxxps://refundkorea[.]cyou/REFUND%20KOREA.apk
• hxxps://bobocam365[.]icu/downloads/pnx01.apk

Since its emergence, this malware has remained undetected by all security solutions, allowing it to operate stealthily. CRIL has identified four unique samples linked to this spyware, all exhibiting zero detection rates across major antivirus engines.

All identified spyware samples were observed communicating with the same Command and Control (C&C) server hosted on an Amazon S3 bucket: hxxps://phone-books[.]s3.ap-northeast-2.amazonaws.com/. Our analysis revealed that the stolen data, including contacts, SMS messages, images, and videos, was openly stored in the S3 bucket (C&C server), further confirming that the malware specifically targeted individuals in South Korea.

The attackers’ poor operational security resulted in the unintentional exposure of sensitive data. We reported the misuse of the AmazonAWS S3 bucket to Amazon Trust and Safety, which disabled access to the URL and made the data no longer accessible. Furthermore, our investigation found no other C&C servers utilizing S3 buckets or exposing stolen data linked to this campaign.

Technical Details

After installation, all spyware samples display a single screen with a message in Korean tailored to the app’s theme.

The source code of this spyware is relatively simple. It utilizes a minimal set of permissions, including “READ_SMS,” “READ_CONTACTS,” and “READ_EXTERNAL_STORAGE,” to carry out its malicious operations. The manifest file specifies only the main activity, which triggers the malicious functionality upon execution.

Upon installation, the spyware requests the necessary permissions; once granted, it executes its malicious functions. These functions, responsible for collecting data from the infected device, are executed within the API method “onRequestPermissionsResult”, as illustrated in the image below.

To exfiltrate images and videos, the malware queries the device’s content provider and uploads each file to the C&C server via the endpoint “/media/+filename”. This behavior is evident in the exposed data, as shown in Figure 3.

The malware gathers contacts and SMS messages from the infected device and stores them in two separate files: phone.json for contacts and sms.json for SMS data. These files are then transmitted to the C&C server, as demonstrated in the figure below.

Conclusion

This campaign highlights the growing sophistication of Android spyware targeting individuals in South Korea. By utilizing an Amazon AWS S3 bucket for Command and Control infrastructure, the threat actors were able to maintain stealth and evade detection for an extended period. This spyware strain utilizes a minimalist approach—leveraging only a few key permissions to exfiltrate sensitive data such as contacts, SMS messages, images, and videos—and demonstrates how even simple malware can be extremely effective.

It is concerning that attackers are increasingly turning to trusted cloud services like AWS as part of their malicious infrastructure. This tactic allows them to bypass traditional security measures and stay under the radar.

Our Recommendations

We have listed some essential cybersecurity best practices that create the first line of control against attackers. We recommend that our readers follow the best practices given below:

• Download and install software only from official app stores like Google Play Store or the iOS App Store.
• Use a reputed anti-virus and internet security software package on your connected devices, such as PCs, laptops, and mobile devices.
• Use strong passwords and enforce multi-factor authentication wherever possible.
• Enable biometric security features such as fingerprint or facial recognition for unlocking the mobile device where possible.
• Be wary of opening any links received via SMS or emails delivered to your phone.
• Ensure that Google Play Protect is enabled on Android devices.
• Be careful while enabling any permissions.
• Keep your devices, operating systems, and applications updated.

MITRE ATT&CK® Techniques

Indicators of Compromise (IOCs)

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