SANS ISC: Bumblebee Malware from TransferXL URLs - SANS Internet Storm Center

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SANS ISC InfoSec Forums

Introduction

Last month, Google's Threat Analysis Group (TAG) reported on EXOTIC LILY using file transfer services like TransferNow, TransferXL, WeTransfer, or OneDrive to distribute malware (link).  Threat researchers like @k3dg3 occasionally report malware samples from this activity.  Based on @k3dg3's recent tweet, I searched through VirusTotal and found a handful of active TransferXL URLs delivering ISO files for Bumblebee malware.

Today's diary reviews an infection generated from this activity on Wednesday 2022-05-18.

Shown above:  Flow chart for infection discussed in this diary.

TransferXL URLs

TransferXL is a legitimate file sharing service.  However, like other services with a cost-free tier, TransferXL has been abused by criminals as a way to distribute malicious files.  However, with TransferXL, we have the benefit of seeing an email address used to share the malicious file.  The image below shows a malicious TransferXL URL recently submitted to VirusTotal.  Viewed in a web browser, it sends a malicious file.  The associated email address is jhurris@wolsleyindustrialgroup.com.

Shown above:  Malicious TransferXL URL delivering malware.

The downloaded zip archive contains an ISO disk image.  When double-clicked, this file is mounted as a DVD drive.  The ISO file contains a visible Windows shortcut and a hidden malware DLL for Bumblebee.  Double-clicking the Windows shortcut will run the hidden malware DLL on a vulnerable Windows host.

Shown above:  Downloaded ISO file mounted as a disk image containing Windows shortcut and hidden malware DLL.

Traffic from an infection

After downloading malware from the malicious TransferXL URL, the infected host generated Bumblebee C2 traffic to 194.135.33[.]144 over TCP port 443.

Shown above:  Initial infection activity with Bumblebee C2 traffic filtered in Wireshark.

Approximately 15 minutes after the Bumblebee C2 traffic first appeared, the infected Windows host generated HTTPS traffic to ec2-3-144-143-232-us-east-2.compute.amazonaws[.]com on 3.144.143[.]242 over TCP port 443.  The infected host sent approximately 5.5 MB of data out and received approximately 4.0 MB of data back from that server.

Shown above:  Encrypted (HTTPS) traffic to an amazonAWS server.

Approximately 14 minutes after HTTPS traffic to the amazonAWS server, HTTPS Cobalt Strike traffic appeared on 23.106.215[.]123 over TCP port 443 using xenilik[.]com as the domain.  It lasted approximately 3 minutes.

Shown above:  Traffic from the infection showing Cobalt Strike activity.

Indicators of Compromise (IOCs)

TransferXL URLs associated with the above email returning zip archives containing malicious ISO files.

• hxxps://www.transferxl[.]com/download/00ZNPDZqZwZ9m
• hxxps://www.transferxl[.]com/download/00jwbtRXtsSsZX
• hxxps://www.transferxl[.]com/download/00vJV4K6QVXSq6
• hxxps://www.transferxl[.]com/download/00y12VGg75h7K
• hxxps://www.transferxl[.]com/download/08j8ZRjHFkVxxc

NOTE: The above URLs usually have ?utm_source=downloadmail&utm_medium=e-mail appended to them.

Email addresses associated with malicious TransferXL URLs:

• andresbolivar@southerncompanygas[.]co
• jhurris@wolsleyindustrialgroup[.]com
• m.jones@wolsleyindustrialgroup[.]com
• mjones@wolsleyindustrialgroup[.]co

Domains from the above emails:

• southerncompanygas[.]co - registered 2022-04-27
• wolsleyindustrialgroup[.]com - registered 2022-04-29
• wolsleyindustrialgroup[.]co - not registered

Malware from an infected Windows host:

SHA256 hash: 1ec8c7e21090fb4c667f40c8720388a89789c569169fe0e41ec81567df499aac

• File size: 669,897 bytes
• File name: TransferXL-00jdMwft3vVZ7Q.zip
• File description: Zip archive retrieved from TransferXL URL

SHA256 hash: 24aa82e1a085412686af5d178810fc0d056c5b8167ae5b88973b33071aa14569

• File size: 1,052,672 bytes
• File name: documents-2205210.iso
• File description: ISO file extracted from downloaded zip archive

SHA256 hash: ade875616534b755f33f6012ea263da808dd7eb50bc903fc97722f37fac7c164

• File size: 1,191 bytes
• File name: New Folder.lnk
• File description: Windows shortcut contained in ISO file
• Shortcut: C:\Windows\System32\rundll32.exe spc.dll,JQhnMKwhpA

SHA256 hash: 88c07354f1d7b0485452d5c39dc1a6d73884e163bc5489c40adc6662602b4d76

• File size: 997,888 bytes
• File name: spc.dll
• File description: 64-bit DLL (hidden flag set) for Bumblebee malware
• Run method: rundll32.exe [filename],JQhnMKwhpA

Traffic from the infected Windows host:

• 194.135.33[.]144 port 443 - Bumblebee C2 HTTPS traffic
• 3.144.143[.]242 port 443 - ec2-3-144-143-242.us-east-2.compute.amazonaws[.]com - HTTPS traffic
• 23.106.215[.]123 port 443 - xenilik[.]com - Cobalt Strike HTTPS traffic

Final words

As the Google TAG blog post notes, EXOTIC LILY is using this method to push Bumblebee malware, and Bumblebee leads to further malware like Cobalt Strike.  And Cobalt Strike has been documented by different sources as leading to ransomware.

Today's diary reviewed a Bumblebee malware infection associated with EXOTIC LILY that led to Cobalt Strike activity.

Pcap and malware samples associated with this infection are available here.

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Brad Duncan
brad [at] malware-traffic-analysis.net