Dubbed Nansh0u, the malicious campaign is reportedly being carried out by an APT-style Chinese hacking group who has already infected nearly 50,000 servers and are installing a sophisticated kernel-mode rootkit on compromised systems to prevent the malware from being terminated.
The campaign, which dates back to February 26 but was first detected in early-April, has been found delivering 20 different payload versions hosted on various hosting providers.
The attack relies on the brute-forcing technique after finding publicly accessible Windows MS-SQL and PHPMyAdmin servers using a simple port scanner.
Upon successful login authentication with administrative privileges, attackers execute a sequence of MS-SQL commands on the compromised system to download malicious payload from a remote file server and run it with SYSTEM privileges.
In the background, the payload leverages a known privilege escalation vulnerability (CVE-2014-4113) to gain SYSTEM privileges on the compromised systems.
"Using this Windows privilege, the attacking exploit injects code into the Winlogon process. The injected code creates a new process which inherits Winlogon SYSTEM privileges, providing equivalent permissions as the prior version."
The payload then installs a cryptocurrency mining malware on compromised servers to mine TurtleCoin cryptocurrency.
Besides this, the malware also protects its process from terminating using a digitally-signed kernel-mode rootkit for persistence.
"We found that the driver had a digital signature issued by the top Certificate Authority Verisign. The certificate – which is expired – bears the name of a fake Chinese company – Hangzhou Hootian Network Technology."
Researchers have also released a complete list of IoCs (indicators of compromise) and a free PowerShell-based script that Windows administrators can use to check whether their systems are infected or not.
Since the attack relies on a weak username and password combinations for MS-SQL and PHPMyAdmin servers, admins are advised to always keep a strong, complex password for their accounts.
