North Korean hackers have been targeting big corporate networks by exploiting the update mechanism of the eScan antivirus software to implant backdoors and deliver the GuptiMiner malware. This sophisticated malware performs a variety of malicious activities including DNS requests to attacker-controlled servers, payload extraction from images, and sideloading malicious DLLs via legitimate software processes. During its execution, GuptiMiner establishes system-level persistence, manipulates DNS settings, injects shellcode into legitimate processes, and uses various techniques to evade detection by security tools.
The infection process is initiated when the malware hijacks the antivirus’s normal update process, substituting the legitimate virus definition package with a malicious one containing the GuptiMiner. This malware, disguised as a DLL file, is executed by the eScan updater, which mistakenly processes the package as a regular update. From there, the DLL fetches additional payloads from the attacker’s infrastructure, enhancing its grip on the infected system.
Additionally, GuptiMiner employs various methods to ensure it operates under the radar. It checks if the infected system has significant computing resources to avoid running in sandbox environments, and it disables running security programs like AhnLab and Cisco Talos products to prevent detection. The malware is designed to deactivate specific security applications, further facilitating its malicious activities without interruption.
Avast researchers suggest that the techniques and infrastructure used by GuptiMiner point to a possible link with the North Korean APT group Kimsuky. Despite eScan’s efforts to enhance security measures by rejecting non-signed binaries and ensuring updates occur over HTTPS, ongoing GuptiMiner infections indicate that older, unupdated eScan clients are still at risk. Avast continues to monitor new infections and has provided a comprehensive list of indicators of compromise to help defenders mitigate this threat.
