The operators behind the Mekotio banking trojan have resurfaced with a shift in its infection flow so as to stay under the radar and evade security software, while staging nearly 100 attacks over the last three months.
"One of the main characteristics […] is the modular attack which gives the attackers the ability to change only a small part of the whole in order to avoid detection," researchers from Check Point Research said in a report shared with The Hacker News. The latest wave of attacks are said to primarily target victims located in Brazil, Chile, Mexico, Peru, and Spain.
The development comes after Spanish law enforcement agencies in July 2021 arrested 16 individuals belonging to a criminal network in connection with operating Mekotio and another banking malware called Grandoreiro as part of a social engineering campaign targeting financial institutions in Europe.
The evolved version of the Mekotio malware strain is designed for compromising Windows systems with an attack chain that commences with phishing emails masquerading as pending tax receipts and containing a link to a ZIP file or a ZIP file as an attachment. Clicking open the ZIP archive triggers the execution of a batch script that, in turn, runs a PowerShell script to download a second-stage ZIP file.
This secondary ZIP file houses three different files — an AutoHotkey (AHK) interpreter, an AHK script, and the Mekotio DLL payload. The aforementioned PowerShell script then calls the AHK interpreter to execute the AHK script, which runs the DLL payload to steal passwords from online banking portals and exfiltrate the results back to a remote server.
The malicious modules are characterized by the use of simple obfuscation techniques, such as substitution ciphers, giving the malware improved stealth capabilities and enabling it to go undetected by most antivirus solutions.
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"There's a very real danger in the Mekotio banker stealing usernames and passwords, in order to gain entry into financial institutions," Check Point's Kobi Eisenkraft said. "Hence, the arrests stopped the activity of the Spanish gangs, but not the main cybercrime groups behind Mekotio."
Users in Latin America are highly recommended to use two-factor authentication to secure their accounts from takeover attacks, and watch out for lookalike domains, spelling errors in emails or websites, and email messages from unfamiliar senders.