Recent reports indicate that threat actors have been using a new type of Linux-targeted backdoor that has never been seen before. This new backdoor has been named SprySOCKS, which uses the strings of Trochilus (Windows backdoor) and the new Socket Secure (SOCKS).
However, this threat vector is carried out by the Earth Lusca threat group. This China-linked attacking group targeted several government departments of foreign affairs, technology, and telecommunications in many countries, including Latin American and African countries.
This threat group has now been found to be targeting the public-facing servers of its victims and exploiting server-based N-day vulnerabilities as part of their operation.
New Linux Malware
On further analyzing the new backdoor, it was discovered that the encrypted file that was found also included some activities of the Derusbi malware as it implemented an interactive Linux shell.
The command and control structure of the protocol was found to be inspired by the RedLeaves backdoor, a remote access trojan (RAT). Moreover, two different payloads were detected consisting of different version numbers, indicating that the malware is still under development.
According to a report shared with Cyber Security News, Earth Lusca is using server vulnerabilities to break into the victim’s network and deploy a web shell. Once inside the network, they install a Cobalt Strike for lateral movement.
Furthermore, the threat group steals documents and email account credentials in order to further deploy advanced backdoors like ShadowPad and Winnti (Linux version) for persistent access into the affected systems.
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Vulnerabilities exploited by Earth Lusca
Earth Lusca leverages several critical and high vulnerabilities relating to an authentication bypass (CVE-2022-40684) and remote code execution (CVE-2022-39952, CVE-2021-22205, CVE-2019-18935, CVE-2019-9670 and CVE-2019-9621).
In addition, a set of three chained vulnerabilities can be combined together for performing a remote code execution. However, products affected by these vulnerabilities include Fortinet (FortiOS, FortiNAC, FortiProxy, and FortiSwitchManager), Zimbra Collaboration Suite, ASP.NET AJAX, GitLab, and Microsoft Exchange.
Trend Micro has published a complete report, which provides detailed information about the exploitation methods, payload components, and Attribution.
Indicators of Compromise
Modified Mandibule Loader
Encrypted SprySOCKS payload (libmonitor.so.2)
SprySOCKS C&C server