Author: Shaul Vilkomir-Preisman
Supporting research: Tom Nipravski
Update: Further developments on how TrickBooster operates is accessible here.
Ever since its discovery in 2016 TrickBot has remained a continuously active and very adaptive actor in the cybercrime threat landscape. What was once a malware family focused on financial data theft is now a robust, elaborate and sophisticated threat, multi-purposed for various types of malicious activity. Recent findings from a currently active and ongoing TrickBot campaign, which features extensive use of signed malware binaries, indicate that it now has a new variant. Alongside its recent addition of a cookie stealing module it has gained a new partner in crime – a malicious email-based infection and distribution module that shares its code signing certificates (details in IOC section below).
The module is employed to harvest Email credentials and contacts from a victim’s address book, inbox, outbox, it can send out malicious spam Emails from the victim’s compromised account, and finally delete the sent messages from both outbox and the trash folder, so as to remain hidden from the user. We believe this module is used by Trickbot for several purposes; prorogation and infection, spreading spam for monetization purposes, and harvesting email accounts which can then be traded and used by other campaigns.
During our investigation of this new module and the network infrastructure associated with it, we were able to access infection servers from which the malware is downloaded onto victim machines, as well as command and control servers. We managed to recover a data base containing 250 million e-mail accounts harvested by TrickBot operators, which most likely were also employed as lists of targets for malicious delivery and infection. The data base includes millions of addresses from government departments and agencies in the US and the UK.
In this blog post we will present our main findings so far based on research conducted in the last 10 days. Our research and analysis into this module, its activity and capabilities continues, and we will update with more details as they become available.
Our investigation started when Deep Instinct detected and prevented a TrickBooster infection attempt using a signed malware binary at a customer environment in the US almost two weeks ago.
Seeing a signed malware binary delivered to a customer environment prompted us to investigate further. We analyzed the malware sample and found swaths of PowerShell code in its memory. Analysis of this PowerShell code immediately led us to the conclusion that we are dealing with a mail-bot.
Following initial analysis, we started looking for more leads on the malware, cross referencing certificate information, sample similarity, and infrastructure used to both deliver and control the malware. We discovered more samples of the malware, both signed and not, additional infrastructure used in the campaign – both to distribute (infection points) and control the malware (C2 Servers). TrickBot samples were also found, signed using the same code signing certificates.
These code signing certificates were apparently issued to various small-to-medium businesses based in the UK. One of which seemingly has very little use for code signing certificates, an air-conditioning, heating and plumbing company, while others do indeed may have a legitimate use for them, according to their registrations.
We continued monitoring the campaign and the infrastructure involved in it, both its infection points and C2 Servers, which were going on and off line, and employing various Geo-IP restrictions and other mechanisms to hamper analysis. It was at one of these servers that we found something that made us realize how successful this campaign is – an Email dump containing approximately 250 million Email addresses.
The recovered Email dump contains massive amounts of commonly used mail provider addresses such as Gmail, Yahoo, etc., but is not limited to these alone. It also contains large amounts of e-mail addresses from various Government departments and other high-profile targets in both the US and the UK.
Other organizations found include universities in the UK and Canada, and several provincial agencies and Governments in Canada.
The numbers of listing for common mail providers were as follows:
Spot checking a few thousands of these compromised Email addresses against previously recorded leaks and breaches, leads us to believe that this is a new mass compromise of e-mails, not previously seen or reported before.
This case, and this significant finding, highlights the success and sophistication of TrickBot, an already very accomplished piece of malware. For a threat actor in the cybercrime sphere, collaborating with a spam malware can bring many possible advantages. Chief among them is the increased ability to distribute your own malware, as spam-bots of all sorts, have been and will likely continue to be, a backbone of malware distribution in general.
As mentioned, TrickBooster is a powerful addition to TrickBot’s vast arsenal of tools, modules and collaborations with other malware. This is not only due to the greatly increased spreading and information harvesting ability, but also due to the cover-up of the ‘implant’ left behind. Following initial deployment of the malware on the victim machine, the implant left behind by the malware, after it finishes initial execution and clean-up goes successfully undetected.
This clean-up is thorough and involves deleting the original infecting executable file, which is a very common practice employed by many malware families. The result is that it is missed by nearly all scanning security vendors, an impressive stealth factor that is much desired among malware operators.
This file, whose main functionality appears to be an e-mail collector targeting OUTLOOK.exe, begins its execution by creating an additional thread where this module is looking for an OUTLOOK.exe window by using “FindWindow” function with “rctrl_renwnd32” as class name (an identifier of the OUTLOOK.exe window).
On the other thread – this module is using COM objects to interact with OUTLOOK.exe. It starts doing so by initializing a COM object (CoInitializeEx) and continuing to interact with it by creating an instance of “Microsoft.Office.Interop.Outlook” with “CoCreateInstance”. It then tries to start OUTLOOK.exe by using “OleRun” function.
When OUTLOOK.exe is executed – this module knows to start interacting with it by using Microsoft Outlook Messaging API (MAPI).
MAPI provides the messaging architecture for Microsoft Outlook 2013 and Outlook 2016. It provides a set of interfaces, functions, and other data types to facilitate the development of Outlook messaging applications. Applications use MAPI to manipulate email data, to create email messages and the folders to store them in, and to support notifications of changes to existing MAPI-related data.
This, and more research and analysis of TrickBooster is still ongoing with more details to be published in the near future.
During our investigation of TrickBooster, we have contacted DigiCert/Thawte, who issued the code signing certificates used to sign both TrickBot and TrickBooster samples used in this campaign and requested their revocation. The offending certificates have been revoked by DigiCert/Thawte.
We are also in the process of reporting and providing details to CERTs and other relevant authorities, and we will work with partners in the community to make available the e-mail address dumps in a secure manner.
Indicators of compromise (IOCs)
Shared Certificate Details
TrickBooster Infection servers (servers known to host TrickBooster executables in this campaign)
TrickBooster Command & Control servers (servers controlling TrickBooster bots involved in this campaign)
220.127.116.11 (likely Command & Control Server)
TrickBooster file hashes (SHA256, involved in this campaign)
FUD TrickBooster “Implant” file hashes (SHA256)
Additional File hash IOCs (SHA256)