The Grandoreiro banking trojan has re-emerged in a global phishing campaign starting March 2024, following a law enforcement takedown in January. This campaign targets over 1,500 banks across more than 60 countries, including regions in Central and South America, Africa, Europe, and the Indo-Pacific. It is believed that the attacks are facilitated through a malware-as-a-service (MaaS) model, indicating a collaboration with other cybercriminals.
Despite Grandoreiro’s initial focus on Latin America, Spain, and Portugal, the current campaign represents a strategic shift, likely due to previous efforts by Brazilian authorities to dismantle its infrastructure. Alongside the expanded targeting, the malware itself has undergone significant updates. These improvements include advancements in string decryption, the domain generating algorithm (DGA), and the ability to exploit Microsoft Outlook clients on infected systems to propagate further phishing attacks.
The phishing attacks start with emails instructing recipients to click a link to view an invoice or make a payment, depending on the impersonated government entity. Clicking the link leads to a fake PDF icon, which downloads a ZIP archive containing the Grandoreiro loader executable. This custom loader, designed to evade anti-malware scans, checks if the host system is in a sandboxed environment, gathers victim data for a command-and-control (C2) server, and downloads the main banking trojan.
Once executed, the trojan establishes persistence via the Windows Registry and uses a reworked DGA to connect with a C2 server for further instructions. Grandoreiro supports various commands for remote system control, file operations, and special modes, including a new module for collecting Microsoft Outlook data and using the victim’s email account to send spam. By leveraging the local Outlook client, Grandoreiro can spread through infected inboxes, significantly increasing spam volume.
