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TrickBot Using Legitimate Looking Sites With SSL Certificates

The TrickBot banking Trojan has been using legitimate SSL certificates alongside websites that closely resemble those of actual banks in recently observed attacks, security researchers warn.

The TrickBot banking Trojan has been using legitimate SSL certificates alongside websites that closely resemble those of actual banks in recently observed attacks, security researchers warn.

Around for only one year, TrickBot has seen numerous updates and added various new capabilities. The malware recently gained worm-like capabilities and began targeting more than just users’ online banking information: it is now also going for Outlook and browser data.

Despite being fake, the sites could easily trick potential victims into believing they are real, especially given the use of servers with full email authentication and HTTPS, Brad Duncan, Palo Alto Networks analyst and handler at the SANS Internet Storm Center, reveals. The Trojan is distributed through malicious emails that use various lures to convince recipients into opening the attached documents.

As part of these attacks, miscreants sent emails from websites closely mimicking those of banks: hsbcdocs.co.uk, hmrccommunication.co.uk, lloydsbacs.co.uk, nationwidesecure.co.uk, natwestdocuments6.ml, santanderdocs.co.uk, santandersecuremessage.com, and securenatwest.co.uk. Almost all of the sites were registered through GoDaddy using various names or privacy services.

The spam emails used HTML attachments designed to download Office documents over HTTPS, in an attempt to evade detection through encrypted network traffic. Once the victim opens the Office document, they are asked to enable macros, which in turn download and execute the TrickBot banking Trojan.

As part of one campaign documented by My Online Security, the malicious emails were pretending to come from Santander Bank, distributed from the convincing look-a-like domain santanderdocs.co.uk. Many of these messages are apparently targeted at small and medium size businesses.

As part of a spam run observed by Cyren, the attackers were impersonating the Lloyds Bank, also using a seemingly correct URL (lloydsbacs.co.uk instead of lloydsbank.co.uk) and a legitimate SSL certificate. Because of the close resemblance with the legitimate URL, the targeted users are unlikely to spot the phishing attempt, especially given the use of an SSL certificate.

The security researchers observed a large number of such emails being sent over a very short period of time: they blocked 75,000 of such messages over a 25-minute period. Most of the messages appeared to be sent from a Dutch IP (5.149.255.107), already a known source of spam and which appears to host many malicious domains, including the one used in this run.

“TrickBot takes the phishing of banking credentials to another level by showing the correct URL of the online bank and confirmation of a legitimate SSL certificate, so even more alert users who pay any attention to these sorts of details will not see anything unusual,” Cyren notes.

The malicious emails have an Excel document attached. Called IncomingBACs.xlsm, the document asks the user to enable included macros, which results in TrickBot being downloaded and installed on the victim’s machine. The version used in these attacks comes with an encoded configuration module in the resource section of its binary and includes support for additional modules that are downloaded from controller domains.

Related: TrickBot Targets Outlook, Browser Data

Written By

Ionut Arghire is an international correspondent for SecurityWeek.

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