September 30, 2023

Operators behind the Grandoreiro banking trojan, which is popular in Latin America, have been using emails posing as the Agencia Tributaria to trick victims into installing the malware.

The campaign began on August 11th, 2020, when many Spanish people receiving messages claiming to be from the Agencia Tributaria. The emails attempted to trick users into believing they were a communication from the tax agency, the messages used sender info like “Servicio de Administración Tributaria” and come from the email address contato@acessofinanceiro[.]com.

The message includes a link that points to a ZIP archive that claims to contain a digital tax receipt and inform the users that they have to fill a document to be submitted to the Agencia Tributaria along with a fee to pay.

“Although the message offers no guarantee of being an official communication, it is likely that some recipients have been tricked into downloading the linked ZIP file via the provided link.”.

“The link redirects to a domain that was registered on the same day. A service that provides identifying information about domain name registrants – the registrant’s country is listed as Brazil, which could perhaps indicate the whereabouts of the operators of this campaign.”

The malicious file has been hosted by threat actors either on a compromised domain or in a cloud storage service like Dropbox. In the case of the cloud storage, the link points to a Dropbox folder containing the ZIP file.

“This ZIP payload contains an MSI file and a GIF image. Homing in on the properties of the MSI file reveals that it was compiled the day before. It should also be noted that the ZIP filename has the country code “ES” at the end.

Researchers also detected other files in Dropbox with very similar sizes and dates of compilation, but with different country codes – possibly indicating that this campaign is targeting victims in various countries at the same time.

The MSI file is as a variant of Win32/TrojanDownloader.Delf.CYA, which is a downloader employed in other campaigns spreading Latin American banking trojans, including Grandoreiro, Casbaneiro, Mekotio and Mispadu.

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