ESET Research uncovers a new threat that targets organizations operating in various sectors in Brazil
Although we have not received any official response from GitHub, when we checked April 6th at around 18:00 UTC, the malicious repositories used by Janeleiro had been taken down.
ESET Research has been tracking a newly discovered banking trojan that has been targeting corporate users in Brazil since 2019 across many verticals affecting sectors such as engineering, healthcare, retail, manufacturing, finance, transportation, and government.
This new threat, which we’ve named Janeleiro, attempts to deceive its victims with pop-up windows designed to look like the websites of some of the biggest banks in Brazil. These pop-ups contain fake forms, aiming to trick the malware’s victims into entering their banking credentials and personal information that the malware captures and exfiltrates to its C&C servers. Janeleiro follows exactly the same blueprint for the core implementation of this technique as some of the most prominent malware families targeting the region: Casbaneiro, Grandoreiro, Mekotio, Amavaldo, and Vadokrist, among others.
In contrast to those well-known malware families, Janeleiro is written in Visual Basic .NET, a big deviation from the favored Delphi programming language that threat actors in the region have been using for years. Janeleiro has been evolving towards the objective of giving more control to the operators to manipulate and adjust its fake pop-up windows based on what they need to pull off the attack, send mouse clicks and keystrokes, and recording user input and the screen in real time. The nature of these types of attack is not characterized by their automation capabilities, but rather by the hands-on approach: in many cases the operator must adjust the windows via commands in real time.
The operators seem comfortable using GitHub to store their modules, administering their organization page, and uploading new repositories every day where they store the files with the lists of C&C servers that the trojans retrieve to connect to their operators. Having your malware depend on a single source is an interesting move – but what if we told you that the newest version of Janeleiro only lives for one day?
Based on our telemetry data, we can affirm that this malware targets only corporate users. Malicious emails are sent to companies in Brazil and, even though we do not think these are targeted attacks, they seem to be sent in small batches. According to our telemetry, the affected sectors are engineering, healthcare, retail, manufacturing, finance, transportation and government.
An example of a phishing email is shown in Figure 1: a false notification regarding an unpaid invoice. It contains a link that leads to a compromised server. The retrieved page simply redirects to the download of a ZIP archive hosted in Azure. Some other emails sent by these attackers don’t have a redirection via a compromised server but lead directly to the ZIP archive.
Figure 1. Example of a malicious email
The servers that host these ZIP archives with Janeleiro have URLs that follow the same convention as other URLs that we saw delivering other banking trojan families (see the Indicators of Compromise section). In some cases, these URLs have distributed both Janeleiro and other Delphi bankers at different times. This suggests that either the various criminal groups share the same provider for sending spam emails and for hosting their malware, or that they are the same group. We have not yet determined which hypothesis is correct.
An overview of the attack is shown in Figure 2.
Figure 2. Janeleiro attack overview (simplified)
The ZIP archive contains an MSI installer that loads the main trojan DLL. Using an MSI installer is a favored technique of several malware families in the region. Janeleiro retrieves the computer’s public IP address and uses a web service to attempt to geolocate it. If the returned country code value does not match BR, the malware exits. If the geolocation check passes, Janeleiro gathers information of the compromised machine, including:
The information is uploaded to a website with the purpose of tracking successful attacks. After that, Janeleiro retrieves the IP addresses of the C&C servers from a GitHub organization page apparently created by the criminals. Then it is ready to start its core functionality and wait for commands from an operator.
In 2020 ESET published a white paper detailing findings about interconnectivity of the most prominent Latin American families of banking trojans including Casbaneiro, Grandoreiro, Amavaldo among others. The similarities described in that paper are in the implementation of the trojan’s core: notifying the operator when there is an active window with an interesting name or title based on a predefined keyword list, and using a fake pop-up window to trick potential victims into thinking they are entering sensitive information on a legitimate website. This process is illustrated by the flowchart in Figure 3.
Figure 3. Typical core implementation of banking trojans from Latin America
Janeleiro follows the exact blueprint for its core implementation as eleven other malware families that target Brazil. As shown in Figure 4, we can see some of the fake pop-up windows created by Janeleiro.
Figure 4. Fake pop-up windows used by Janeleiro
Janeleiro begins enumerating windows and checking their titles to find interesting keywords (as shown in Figure 5) that would indicate that the user is visiting the website of a banking entity of interest, especially those that are supported by its implementation of fake pop-up windows.
Figure 5. List of keywords that Janeleiro searches for in window titles
When one of the keywords is found, Janeleiro immediately attempts to retrieve the addresses of its C&C servers from GitHub and connects to them. These fake pop-up windows are dynamically created on demand and controlled by the attacker via commands to the malware, as they go through several stages to trick the user while the attacker, in real time, receives screen captures, the logged keystrokes and information that is entered in the fake forms.
The fact that threat actors abuse GitHub is nothing new; however, Janeleiro does it in quite interesting ways: the operators have created a GitHub organization page that they rename every day in the form SLK<dd/mm/yyyy> where <dd/mm/yyyy> is the current date.
A screenshot of the GitHub organization page as it looked on 15 March 2021 is shown in Figure 6.
Figure 6. GitHub organization page with repositories used by the operators of Janeleiro
Daily, the operator novoescritorio1-alberto creates a new repository following this naming format. The purpose of the repository is to contain a file that has the list of IP addresses for Janeleiro’s C&C servers where it connects to report to its operators, to receive commands and to exfiltrate information in real time.
A screenshot showing one of the repositories in the GitHub organization page attributed to Janeleiro’s operators is shown in Figure 7, including the username of the account that does the commits.
Figure 7. Main branch with the SLK file for Janeleiro version 3
A screenshot of the secondary branch in the repository is shown in Figure 8.
Figure 8. SLK branch with the SLK file for Janeleiro version 2
We have notified GitHub of this activity but at the time of writing no actions have been taken against the organization page nor the account that creates the repository with new C&C server addresses.
In the newest version of Janeleiro, version 0.0.3, the developers introduced an interesting encryption/decryption feature using an open-source library called EncryptDecryptUtils. The new procedure for decryption is shown in Figure 9.
Figure 9. Procedure for decryption implemented by Janeleiro version 0.0.3
To decrypt a string, Janeleiro encrypts the string resulting from the current date and the result is then used as a passphrase and salt value to create a new key for decryption. This has an extremely important effect: the newest version of Janeleiro can only decrypt its strings on one intended day. That could be the same day the strings were encrypted or one day in the future; on any other day, the decryption fails.
This is also true for the contents of the SLK file in the main branch: the encrypted and base 64 encoded list of C&C servers as shown in shown in Figure 10.
Figure 10. Contents of the SLK file in the main branch.
The contents are encrypted with the same procedure: when Janeleiro decrypts the contents of the file it must be on one specific date – the current date – to work as intended.
Janeleiro has an internal version value (as shown in Figure 11) that can be used by the attackers to identify which version of their malware successfully compromised a machine. As of March 2021, we have identified four versions, but with two of them sharing the same internal version number.
Figure 11. Configuration values used by version 0.0.2A from 2020
While in 2021 we have seen versions 0.0.2 and 0.0.3, we were interested in finding a missing key piece in the evolution of Janeleiro: version 0.0.1, which should have been in existence in late 2019 or early 2020. To our surprise we found version 0.0.4 samples instead dating to 2019. These new samples of the trojan were deployed by a DLL loader component in tandem with a password stealer, which means the group behind Janeleiro has other tools in their arsenal.
An overview of Janeleiro’s versions from 2019 through 2021 is shown in Figure 12.
Figure 12. Janeleiro’s strange evolution timeline, based in the internal version of the malware
The inconsistency in the timeline and internal versioning of the malware suggests that it was under development as far back as 2018, and in 2020 they decided to switch to a previous version of their code and to improve that and refine its command processing for the operator to have better control of the trojan during the attack.
While Janeleiro follows the same blueprint for the core implementation of its fake pop-up windows, along with other malware families that ESET has documented in the region, it sets itself apart from those malware families in several ways:
Commands with parameters are received from the C&C server in encrypted form with the same algorithm used to encrypt strings (see section Appendix A). A typical command format is like this: %CommandName%%PredefinedSeparatorKeyword%%Parameters%.
After decryption the command is split into an array of strings; each part of the command is separated by a predefined keyword hardcoded in the malware’s configuration – all versions we analyzed use |’meio’|, which separates the command name and each parameter.
Figure 13 shows how Janeleiro checks the name of the command and executes the requested action.
Figure 13. Example of Version 0.0.2B processing command startinfo
When Janeleiro sends data back to the operator, it does it in a similar format: %CommandName%%PredefinedSeparatorKeyword%%Encoded data%.
The majority of Janeleiro’s commands are for controlling windows, the mouse and keyboard, and its fake pop-up windows. As the development evolved from Version 0.0.2A to 0.0.3, more commands were added that offered the operator a more refined control:
The experimental nature of Janeleiro, going back and forth between different versions, tell us about an actor who is still trying to find the right way to do it but is no less experienced than the competition: Janeleiro follows the unique blueprint for the core implementation of the fake pop-up windows as many LATAM banking trojans, this does not seem to be a coincidence or inspiration: this actor employs and distributes Janeleiro sharing the same infrastructure as some of the most prominent of these active malware families. As we continue to track the activities of this actor, time will tell what new developments they will come up with in the future.
For any inquiries, or to make sample submissions related to the subject, contact us at firstname.lastname@example.org.
Special thanks to Johnatan Camargo Zacarias from Itaú bank for his help with the investigation.
A comprehensive list of Indicators of Compromise (IoCs) and samples can be found in our GitHub repository.
|SHA-1||Description||ESET detection name|
In the following <NNNNNNNNNNN> is a random number between 10000000000 and 90000000000.
These are the IP addresses of the C&C servers where Janeleiro connects to report, receive commands and send data:
These are the tracking URLs where Janeleiro sends information about the compromised system during installation:
These are the URLs used by System.Logins.dll to exfiltrate the harvested data:
IPs associated with the domain:
Note: This table was built using version 8 of the MITRE ATT&CK framework.
Here is each incarnation we have found of Janeleiro from 2019 until March 2021.
Both LoadDllMSI.dll and LoadSystem.dll perform the same tasks:
System.Logins: It is a password stealer for Google Chrome, FileZilla, Mozilla Firefox, Opera, Pidgin, and Mozilla Thunderbird. Additionally, it harvests email information from Gmail. All the information is exfiltrated to two websites. Version 0.0.4 is the only one that is deployed with this malicious tool.
System.Modules: Janeleiro’s main trojan, implemented as a Windows Forms application compiled as DLL. This version had the capacity to dynamically create fake pop-up windows using several Forms for several banking entities, including banks operating in Mexico, but it is unknown if this version was distributed in Mexico at any point.
This version used two GitHub organization pages to download the IP addresses of its C&C servers: the names of the pages are generated by encrypting the current date with SLK as suffix as shown in Figure 14.
Figure 14. Version 0.0.4 attempts to read file in a GitHub repository that contains the encrypted list of C&C servers
At the time of writing, we believe that the operators have abandoned this version of the malware. We couldn’t find any active GitHub pages by following the name generation algorithm used by Janeleiro.
Many commands for the trojan were left unimplemented, some were implemented and other discarded in newer versions used in 2020 and 2021.
The MSI installer loads a DLL that borrows from LoadSystem installation and persistence procedures but unpacks the embedded main trojan DLL from its resources. The main trojan was implemented as a Windows Forms application compiled as DLL.
This version of Janeleiro only uses one Form to create the fake pop-up windows with more commands supported by the operator but with fewer targets: Mexican banking entities were discarded. All of the images used to cover the screen and trick the user are for Brazilian banks.
This version also appears to have been abandoned and cannot contact its C&C servers by retrieving the IP lists from a GitHub page. It uses the same algorithm as Version 0.0.4 with the same key vhpjzqqtpo, suggesting that the operators where using the same GitHub page as for Version 0.0.4. Figure 15 shows the code that attempts to retrieve the list from GitHub.
Figure 15. Version 0.0.2A attempts to download a new list of C&C servers from a repository on a GitHub organization page
New characteristics of this version:
Figure 16 shows the implementation of clipboard hijacking by Janeleiro; when a bitcoin address is found, it randomly picks one from its own list of bitcoin addresses and replaces it.
Figure 16. Janeleiro’s implementation of clipboard hijacking
In this version a simplified procedure was implemented to retrieve the addresses of its C&C servers from a GitHub organization page; the name scheme this time is a simple concatenation of SLK with the current date time without the slashes, as shown in Figure 17.
Figure 17. Version 0.0.2B procedure to retrieve its list of C&C servers. We have decrypted some strings for clarity.
The code attempts to download the contents of a file in a secondary branch. The file contains, in plaintext, the list of the C&C IP addresses and ports. At the time of writing, the GitHub organization pages can be found using the procedure as they continue to operate with this recent version of Janeleiro.
New characteristics of this version:
This version uses the same procedure as Version 0.0.2B to get the C&C servers from the GitHub organization page, with the difference that it uses the main branch within the repository and the list is encrypted and encoded with base64 as shown in Figure 18.
Figure 18. Main repository containing an encrypted list of C&C servers
This procedure is also used when decrypting the list of C&C servers, therefore there must exist a repository containing the file in the main branch, with the encrypted list intended for that day. Otherwise this version cannot contact the operators as decryption will fail.
Janeleiro uses several third-party, open-source libraries for various purposes: