APT37 Hackers Exploit Group Chats to Deliver Malicious LNK Files

In 2024, South Korea witnessed an alarming surge in Advanced Persistent Threat (APT) attacks, with the state-sponsored APT37 group emerging as a significant threat actor.

Leveraging sophisticated techniques, the group targeted individuals and organizations through malicious Hancom Office HWP documents and LNK files distributed via K Messenger group chats.

These attacks primarily aimed to evade antivirus detection while exploiting trust-based communication channels.

On November 13, 2024, two malicious files were disseminated in a K Messenger group chat: an HWP document titled The Impact of North Korea-Russia Closeness on the North Korean Regime and a ZIP file containing an LNK shortcut.

The attackers utilized spear phishing to gain initial access, followed by reconnaissance and lateral movement within compromised systems.

By impersonating trusted contacts, the attackers exploited victims’ familiarity to distribute additional malware.

The HWP files contained Object Linking and Embedding (OLE) objects that triggered malicious PowerShell commands upon execution.

Similarly, the LNK files disguised as legitimate documents embedded harmful scripts targeting Windows environments.

Although Android devices were relatively unaffected, users were cautioned against installing unauthorized APK applications.

Sophisticated Malware Techniques

APT37’s tactics included embedding multiple OLE objects within HWP files to execute hidden batch scripts like “lexus.bat” and “bus.dat.”

These scripts employed XOR logic to decode shellcode, enabling fileless in-memory execution of RoKRAT malware.

The RoKRAT module facilitated data exfiltration via pCloud’s API token while enabling remote control over infected systems.

The attackers also exploited document themes such as lecture materials or business correspondence to deceive victims.

For instance, emails impersonating the Korea Aerospace Research Institute distributed malicious HWP files under titles like Status of AI Utilization by Major Countries.

These targeted drone research institutions and universities, further underscoring the group’s strategic objectives.

Countermeasures

To mitigate such threats, experts emphasize deploying Endpoint Detection and Response (EDR) systems capable of identifying abnormal terminal behavior.

Genian EDR solutions have proven effective in detecting and blocking malicious HWP documents by analyzing office software’s process execution patterns.

Additionally, anomaly-based rules have been instrumental in identifying fileless malware operations communicating with Command-and-Control (C2) servers.

Organizations are advised to enforce strict security policies, including regular employee training on phishing awareness and limiting computer access when unattended.

Furthermore, scrutinizing email attachments and messenger-transferred files remains critical in preventing infiltration.

The APT37 group’s evolving tactics highlight the need for robust cybersecurity frameworks to counteract state-sponsored cyber threats effectively.

By adopting proactive measures, organizations can better safeguard against these sophisticated attacks.

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