The latest version of financial Trojan TrickBot adds a new trick: stealth code injection through macro-enabled Microsoft Word documents.
The TrickBot malware first emerged in 2016. As noted by security firm Cyberbit, new iterations “have appeared on an ongoing basis, each time updated with new tricks and modules.” The latest version, which was used in North American and European banking attacks at the beginning of August, employs stealth code injections using Microsoft Word documents.
Victims receive an email with an attached Word document that contains macro code. To evade detection, TrickBot’s users have designed the macro to execute only if users click “enable content” and then resize the document by zooming in or out. According to Cyberbit, while this method will likely evade sandboxes, it may also limit infection numbers since not every user will attempt to zoom the document. Once initiated, the malware “sleeps” for 30 seconds — another attempt to evade detection — and then runs an obfuscated PowerShell script to download and execute TrickBot.
Tricks of the Trade
While the macro injection mode is new, TrickBot’s core functions remain unchanged. For financial organizations and end users, infection leads to Windows Defender modifications — the TrickBot malware disables real-time monitoring to reduce the chance of detection — along with direct function calls using system cells. These processes improve the malware’s ability to evade both security services offered by Windows and third-party monitoring tools.
Once up and running, TrickBot goes after browser and Microsoft Outlook data, gathers system and network information, steals domain credentials, and can prevent victims from accessing their computers.
How Can Users Avoid TrickBot Malware?
To counter the impact of evolving Trojans like TrickBot, IBM X-Force recommends updating all applications and antivirus solutions to increase the chances of detection. In addition, users should always verify through a separate channel the legitimacy of any unsolicited email attachments before they’re opened. As noted above, TrickBot malware only works if users enable Macros and zoom in or out of the document; if the document is never opened, no compromise occurs.
IBM experts also suggest implementing email security best practices to help limit the spread of Trojans and other malware. These include conducting regular phishing simulations to discover the state of user security awareness and employeeing managed security services (MSS) to evaluate existing security measures and deploy integrated solutions such as spam detectors, antivirus tools and email encryption.