Early this year, Trend Micro investigated a security breach suffered by a company in Taiwan. Threat actors employed a custom Cobalt Strike loader in the attack. Further analysis, revealed that the same threat actor targeted multiple regions using a similar Cobalt Strike loader and has been active since 2020. The experts attributed the attacks to a new subgroup of the China-linked APT41 group, tracked as Earth Longzhi.
The researchers analyzed two campaigns attributed to Earth Longzhi; the first one conducted between 2020 to 2021 targeted the government, infrastructure, and health industries in Taiwan and the banking sector in China. The second campaign from 2021 to 2022, targeted high-profile victims in the defense, aviation, insurance, and urban development industries in Taiwan, China, Thailand, Malaysia, Indonesia, Pakistan, and Ukraine.
The new APT group used spear-phishing emails as an attack vector to deliver Earth Longhzhi’s malware. The malware was embedded in a password-protected archive attached to the messages. In other cases, attackers shared a link to a Google Drive hosting a password-protected archive containing a Cobalt Strike loader called CroxLoader.
In another attack scenario, the group exploited publicly available applications to deploy and execute a downloader, which downloads a shellcode loader and the necessary hack tools for the routine.
The researchers noticed that the new APT targets organizations that in the past were hit by another group of APT41 known as Earth Baku.
“After checking all the metadata of the Cobalt Strike payloads, we found that most of payloads shared the same watermark, 426352781, and public key 9ee3e0425ade426af0cb07094aa29ebc. This watermark and public key combination is also used by Earth Baku and GroupCC, which are also believed to be subgroups of APT41. The identified watermark has not yet been attributed to other threat actors.” reads the analysis published by Trend Micro. “The use of the same watermark and public key indicates Earth Longzhi sharesing the Cobalt Strike team server, as well as Cobalt Strike package and license with the other APT41 subgroups.”
The investigation into the second campaign revealed that the Earth Longzhi APT used multiple custom versions of known hacking tools used for privilege escalation (PrintNightmare and PrintSpoofer), credential dumping (custom standalone Mimikatz), and disabling security products. Instead of using public tools as they are, the threat actors are able to reimplement or develop their own tools based on some open-source projects. In the following subsections, we introduce these hack tools.
“In the process of attribution, we also discovered that the group uses shared Cobalt Strike licenses and imitates the TTPs used with other APT41 subgroups.” concludes the report. “The behavior of sharing tools between different groups could point to the following circumstances:
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(SecurityAffairs – hacking, Earth Longzhi)