Attackers Spread Dridex Banking Trojan Via Malicious Macros

Researchers at Trustwave have identified an attack campaign using macros that is targeting banking customers in the U.K. – yet another example of attackers leveraging the technique.

The attack works this way – the victim gets an email with a Microsoft Word or Excel document attached. The document includes a payload that downloads malware called ‘Dridex’, which is designed to target online banking information. The attacks lure the victims to open the attachment by using the names of legitimate companies located in the U.K. Some of the emails refer to an ‘attached invoice’ by stating it comes from a software company, online retailer or bank.

Once the user opens the attachment, Dridex malware is installed. Users must enable macros in order for the malicious documents to work, and the some of the documents contain instructions on how to do just that. 

Researchers at Microsoft recently reported a spike in threats using macros during the month of December.  Specifically, Microsoft spotted two macro downloaders spreading through spam email campaigns: TrojanDownloader: W97M/Adnel and TrojanDownloader:O97M/Tarbir. The threats appear to be targeting Microsoft customers predominantly in the US and UK.

“Using macros in Microsoft Office can help increase productivity by automating some processes,” according to the Microsoft Malware Protection Center. “However, malware authors have also exploited these capabilities. Since Microsoft set the default setting to “Disable all macros with notification”, the number of macro-related malware threat has declined. More recently we have seen new threats emerging that include some form of social engineering to convince users to manually enable macros and allow the malicious code to run.”

According to Microsoft’s statistics, the number of Adnel and Tarbir encounters spiked in the middle of December. The spam emails are being spread using subject lines related to finances, such as ‘ACH Transaction Report’, ‘Invoice as requested’ and ‘Payment Details’.

Like Microsoft, Trustwave also detected a spike in macro-related threats late last year. In particular, the firm found that the volume of macro-document based spam spiked in October and then fell before reaching a peak in mid-November. It then fell again and jumped again in mid-December.