TrickBot Featured in New Wave of Phishing Emails Signaling Renewed Use of this Botnet Malware

The TrickBot financial crimes and botnet malware has seen mild usage since its introduction in late 2016. While it is able to emulate many of the features that made the Dyre trojan so successful, many aspects of its deployment left it rough around the edges. Examples of this roughness like persistence via a scheduled Windows task named “Bot” limited this malware’s evasion and anti-forensic capabilities. Furthermore, previous deliveries leveraged relatively simplistic techniques such as relying on executables in archives attached to phishing emails securing new infections. However, with some very minor refinements to both the malware resident and delivery processes, threat actors have evidenced a renewed drive to explore the possibilities this malware tool has to offer. The exploration of malware technologies and delivery processes are both trends that have been previously addressed in PhishMe® reporting and, as threat actors continue to turn to commoditized delivery methods, will continue to evolve.

TrickBot is a robust financial crimes and botnet trojan that shares a number of characteristics with the infamous Dyre banking trojan. Despite sharing similar functionality, TrickBot is an approximation of Dyre, not an exact copy. While this extends to the theft of online banking credentials, this botnet tool is flexible enough to provide threat actors with the ability to adapt and customize their intrusion based on information collected about machines infected by TrickBot.

One of the most tenacious and recurring delivery methodologies featured within the current threat landscape is the combination of PDF documents with an embedded Microsoft Word document. This document in turn contains macro scripting used to download and deobfuscate an XOR-ciphered executable payload. A number of current top-tier malware varieties have been deployed using this methodology. Criminals delivering the Jaff encryption ransomware and before it the Locky encryption ransomware both harnessed this technique as have the Dridex threat actors. This technique is popular because it provides some advantages over using a PDF or Word document with macros alone. The first and most obvious is the appearance it presents to its recipients. While awareness of Word documents with macros has proliferated in recent years due to its prolific use in phishing attacks, by adding just one step, unprepared users can be convinced to engage with the infection method.

Figure 1 – PDF reader requests permission to extract and open a Word document as seen with Jaff, Locky, and Dridex

This technique has now been employed as a means of delivering the TrickBot malware along with a renewed use of standalone Office documents with macro scripting. The phishing emails delivering these infection utilities featured no message content, no narrative, and in some cases, no subject line. This employs a different social engineering technique that, rather than relying on persuasive argumentation, appeals to the recipient’s curiosity.

Attachment Filename MD5 Hash
11180651.pdf d397901e0d35a108ed4218715e47f79d
89049517.pdf b327868a11287995c32dc433dbeb3fb7
61783306.pdf bb42465392dbc15c1b4ed88ab6ed47b3
33238593.pdf b0f75286403bd759872bde9655c76038
SCAN_0221.doc ed1e1515dcc0d8a7608e73345de642ea
SCAN_9392.doc e9d181fbbe7d10bf2b17672b4966ae70
SCAN_4659.doc 4596f215c4760cd643fc79935fd41736
SCAN_1146.doc c019021cf3473e46395791ca18e2dd82

Figure 2 – Example indicators from campaigns using this attack method

However, this renewed threat actor utilization also brings a very subtle refinement to the overall polish of the TrickBot deployment intended to improve its rate of successful infection as well as its likelihood to persist undetected on infected endpoints. The TrickBot malware relies on a Windows Task to ensure its persistence within infected environments. This task is defined by an XML file written to disk after TrickBot is initially run. Early examples of this persistence task were named “Bot” and would show up as such during audits of system tasks. However, this most recent iteration of task from “Bot” to the much less obvious “services update”. While this refinement may seem insignificant, it portends a much more serious approach on the part of the threat actor. One of these two filenames would look entirely out of place within an infected environment while the latter would be more reasonable–perhaps reasonable enough to escape detection.

Figure 3 – An excerpt from the “services update” Windows task

This renewed interest and exploration into distribution of the TrickBot malware comes with a handful of refinements in delivery and persistence. By harnessing a successful distribution methodology and refining their persistence mechanism, criminals using TrickBot are attempting to take their success using this botnet malware to another level. The challenge for security professionals is to develop a comprehensive defense against these improvements. The best approach is to combine tactical observations and atomic indicators with a strategic view of threat actors’ goals. Ultimately, defenders should not focus on just one attack vector or malware tool, but instead should anticipate the strategy threat actors use to accomplish their mission. In many cases, this mission is predicated upon the success of phishing emails.

Understanding how attackers craft and deploy these emails allows an organization to prepare and empower the email users within their organization. These users can then engage critically with those messages and, when a suspicious email is detected, report it to the security and incident responders defending the enterprise. These internal reports can then be compared to and combined with external sources to help network defenders overcome threats at a tactical level and apply those tactics as part of a greater strategy to overcome any phishing threat.

Learn about emerging trends and evolving threats in phishing malware with PhishMe’s Q1 Malware report, click here to download.

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