The Lazarus Group, a state-backed hacking group linked to North Korea, has been identified targeting vulnerable Windows Internet Information Services (IIS) web servers as part of their cyber espionage and financial motivation activities.
South Korean researchers at AhnLab Security Emergency Response Center (ASEC) discovered this latest tactic, which allows the group to gain initial access to corporate networks. IIS servers, commonly used by organizations for hosting web content, can act as entry points if poorly managed or outdated.
Lazarus exploits known vulnerabilities or misconfigurations in IIS servers, using DLL sideloading techniques to execute their attacks and avoid detection by antivirus tools. They drop legitimate files and encoded files on the servers, leveraging them to launch malicious code and gain control.
The initial stage of Lazarus’ attack involves creating files on IIS servers using the w3wp.exe process, including a legitimate file, ‘Wordconv.exe,’ and a malicious DLL, ‘msvcr100.dll.’ These files are used to decrypt and execute the malicious payload in memory, evading antivirus detection.
The researchers at ASEC have found similarities between ‘msvcr100.dll’ and a previously observed malware used by Lazarus, suggesting a new variant of the same malware. In the second phase, Lazarus exploits a Notepad++ plugin to create another malware, ‘diagn.dll,’ which decrypts and executes a payload encoded with the RC6 algorithm. Although the exact purpose of this payload is unknown, evidence points to credential theft activities.
During their attack, Lazarus performs network reconnaissance and lateral movement, using valid user credentials likely obtained in the previous step. Port 3389 (Remote Desktop) is commonly exploited for lateral movement.
However, ASEC has not identified any further malicious activities following the lateral spread on the network. Given Lazarus’ reliance on DLL sideloading, ASEC advises organizations to monitor abnormal process execution to detect and prevent the group from carrying out activities such as information exfiltration and lateral movement.
This discovery sheds light on the evolving tactics of the Lazarus Group and highlights the importance of maintaining strong security measures, particularly for IIS servers, to defend against advanced cyber threats.
