Recent FakeBat Activity Observed in December 2022

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Here’s the latest from our TRU Team…

This blog was updated in September 2023 based on research from TRU that identifies this as FakeBat. This blog originally identified this threat as BatLoader.

What did we find?

• FakeBat is a Malware-as-a-Service (MaaS) first advertised on Exploit Forums in December 2022.
• FakeBat is delivered via malicious advertisements, commonly Google Search Ads, for popular software.
• Recent activity used signed MSIX installation packages to deliver malware.

This blog will focus on a recent activity cluster identified in mid-December 2022.

Recent FakeBat Activity

On December 16^th, 2022, eSentire’s Security Operations Center responded to several FakeBat infections impacting customers in the financial services and higher education sectors.

In both cases, FakeBat was distributed via a lookalike website for WinRAR:

Figure 1 FakeBat WinRAR lookalike page.

The download link leads to ads-check[.]com, which serves a 302 redirect to down[.]software. The latter responds with a MSI payload file masquerading as the WinRAR utility. Ads-check[.]com is used in multiple stages of FakeBat’s infection chain to track infection sources and progress. The site uses a Russian language login panel:

Figure 2 Ads-check[.]com’s Russian-language admin panel.

The second website in the payload delivery chain, down[.]site contains JavaScript logic for displaying a greeting in either English or Russian based on the user’s browser preferences.

Figure 3 down[.]software JavaScript

According to available data on VirusTotal, the site has been active since late November 2022 and has delivered payloads impersonating WinRAR, Awesome Miner, uTorrent and LightShot.

Figure 4 VirusTotal records for down[.]software.

The initial payload (winrar-x64-611.msi) is a Microsoft Software Installer file created with Advanced Installer. The MSI file is configured to run on systems with at least 4GB of memory and an active Internet connection.

Figure 5 FakeBat PowerShell scripts via Advanced Installer's Custom Actions

The installer file has 5 Custom Actions (above) which use PowerShell to fetch code from Hugging Face, an American AI company whose website offers a code repository for community projects:

Figure 6 PowerShell scripts hosted on Hugging Face.

The DownGPG Custom Action uses PowerShell to retrieve and execute a second PowerShell command. This command downloads and saves two encrypted payloads (Redline and Ursnif).

Figure 7 Custom Action PowerShell command “DownGPG”

The two payloads are hosted on the Bitbucket code repository. The “Downloads” field indicates both files have been downloaded thousands of times since December 1^st (how many were legitimate victims is not known).

Figure 8 Secondary FakeBat payloads hosted on BitBucket.

The DownOfficial Custom Action retrieves the Nsudo and WinRAR from their respective download sources. It saves both to the user’s AppData directory.

Figure 9 Custom Action PowerShell command “DownOfficial”

The Stup Custom Action is similar to “DownGPG” – it retrieves an encoded PowerShell command that connects to the ads-check[.]com C2 to likely signal infection start.

Figure 10 Custom Action PowerShell command “Stup"

Stup_1 sleeps then adds .rar, .cmd, .bat, .zip and .exe to Windows Defender exclusions for file extensions.

Figure 11 Custom Action PowerShell command “Stup_1"

Stup_2 excludes several paths and processes from Windows Defender. The process exclusion list includes the two payloads (Redline and Ursnif) and Explorer.exe process, which is likely a target for code injection for Ursnif.

Figure 12 Custom Action PowerShell command “Stup_2"

The Custom Action Final is a PowerShell script that most closely resembles past FakeBat scripts. It contains the function to install GPG4Win as well as encryption and decryption functions. These functions are seemingly identical to past FakeBat scripts and was likely copied from the GitHub repository.

Figure 13 Custom Action PowerShell script “Final"

This section calls the above functions to install GnuPG to AppData, decrypts the payloads using the password ‘putingod’, and executes the two unencrypted payloads with elevated privileges using Nsudo. Finally, it calls home to the ads-check[.]com C2 (likely to record the install).

Figure 14 Bottom section of PowerShell script from "Final" Custom Action.

Decrypted Payloads

Both payloads were gpg-encrypted using the password “putingod”.

ZipCosdaz.exe (4a57cbce13def4a4d9f7bccc49a8af52) is a .NET loader that retrieves Redline Stealer from 193.56.146.114/pdfbuild.exe. Redline connects to C2 Address 193.56.146[.]114:44271.

Figure 15 Snippet from .NET Loader "ZipCosdaz.exe"

ZipCosdaz1.exe (c03be50c6fbfd3aec108a7bcd7aaea82) is a loader for Ursnif malware. It stages HTA/PowerShell commands in HKCU\\Software\AppDataLow\Software\Microsoft\{GUID} and injects into Explorer.exe process using PowerShell.

This is the isfb_v2.14+ variant configured to connect to the following C2 domains:

45.11.182.97

79.132.128.108

91.241.93.98

79.132.128.109

91.242.217.28

91.241.93.111

Memory strings include basic living-off-the-land discovery commands common with precursor threats. It should be noted that this variant is not RM3/LDR4, which is suspected to be a precursor for ransomware attacks.

Figure 16 Snippet of Ursnif memory strings

How did we find it?

• eSentire’s MDR for Endpoint identified code decryption and execution behavior associated with FakeBat.

What did we do?

• Our team of 24/7 SOC Cyber Analysts contained affected systems and notified customers.

What can you learn from this TRU Positive?

• Drive by social-engineering attacks remains a popular vector for a variety of malware loaders. FakeBat makes use of several delivery methods, primarily malvertising and fake software downloads from TRU’s observations.

• In recent occurrences, FakeBat delivered both Ursnif and Redline Stealer for monetizing the infected endpoint. This approach enables monetization through fraud as a baseline while leaving the door open for hands-on-keyboard attacks.
• Ursnif is traditionally a banking trojan which, unlike competitors such as IcedID, Emotet and Qakbot, has not transitioned to focus on extortion attacks in recent years. This appears to be changing per the operators of at least one Ursnif variant.
  • Recent interview with operators of the RM3 botnet and new Ursnif variant “LDR4” indicate the group is focusing exclusively on extortion attacks, given the complexity of maintaining and operating banking fraud schemes. However, the Ursnif variant observed in recent FakeBat incidents was neither of these variants.

Recommendations from our Threat Response Unit (TRU):

• Raise awareness of malware masquerading as legitimate applications, and include relevant examples within your Phishing and Security Awareness Training (PSAT) program to educate your employees on how to protect themselves against similar cyber threats. Remember – an effective PSAT program emphasizes building cyber resilience by increasing risk awareness, rather than trying to turn everyone into security experts.
• Protect endpoints against malware.
  • Ensure antivirus signatures are up-to-date.
  • Use a Next-Gen AV (NGAV) or Endpoint Detection and Response (EDR) product to detect and contain threats.

eSentire’s Threat Response Unit (TRU) is a world-class team of threat researchers who develop new detections enriched by original threat intelligence and leverage new machine learning models that correlate multi-signal data and automate rapid response to advanced threats.

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