Introduction

Trickbot malware has been a relatively constant presence in the cyber threat landscape so far this year.  We've seen activity continue this week, and today's diary reviews an infection I generated on Wednesday 2021-02-17.

The infection chain of events:

The email

Shown above:  Screenshot from an example of malspam seen earlier today (Wednesday 2021-02-17).

The spreadsheet

Shown above:  Screenshot of the attached Excel spreadsheet with macros for Trickbot.

Infection traffic

Shown above:  Traffic from an infection filtered in Wireshark.

Forensics on an infected Windows host

Shown above:  Initial Trickbot binary retrieved by the Excel macro.

Shown above:  Scheduled task for Trickbot.

In the above image (double-click on it to get a higher-resolution picture), you can see the Trickbot DLL is not where the scheduled task points to.  When I restarted the infected host, it gave me an error saying it couldn't run the task.  I've noticed this during the past several months from Trickbot infections that use a DLL file as the initial binary.  Unfortunately, I don't know why this happens.

Indicators of Compromise (IOCs)

EXAMPLES OF SUBJECT LINES AND REPLY-TO ADDRESSES:

• Subject: DocuSign: Equipment # 1332
• Subject: DocuSign: Equipment # 9448
• Subject: DocuSign: Equipment # 9722
• Subject: DocuSign: Equipment # 12169
• Subject: DocuSign: Equipment # 23863

• Reply-To: Lease Consultants <cloying@docusign.net>
• Reply-To: Lease Consultants <dianoetic@docusign.net>
• Reply-To: Lease Consultants <modicum@docusign.net>
• Reply-To: Lease Consultants <omidyar@docusign.net>
• Reply-To: Lease Consultants <rumery@docusign.net>

• Note: Sending addresses may have been from email accounts that were compromised.

FILE HASHES FROM ATTACHMENTS SUBMITTED TO VIRUSTOTAL:

MALWARE FROM AN INFECTED WINDOWS HOST:

SHA256 hash: bc033032b6d2afcea2a07f4b5eb5de3137c9fc83c1302fe28a781137168884eb

• File size: 168,960 bytes
• File name: DocuSign_1993467225_1309843348.xls
• File description: Excel spreadsheet with macros for Trickbot gtag rob13

SHA256 hash: e1b67bd8b15bcd422fcbc74fa3b691c40c527ffedc951a6bb8e67ca257240d16

• File size: 698,880 bytes
• File location: hxxps://destinostumundo[.]com/layout/recruter.php
• File location: C:\Users\[username]\HGrt.foste
• File description: Initial Trickbot gtag rob13 binary (DLL file)
• Run method: rundll32.exe [file name],DllRegisterServer1

SHA256 hash: 24bd33f4ba457d77d796620a2cd4b7a3e38d63e2286fec752d898ab7c5204e4b

• File size: 864,256 bytes
• File location: hxxp://195.123.208[.]170/images/control.png
• File description: Follow-up Trickbot EXE file, gtag tot43

SHA256 hash: f0391039f888fb30566295365420868ac8539075e25a690ac4400a8bb91eb803

• File size: 864,256 bytes
• File location: hxxp://195.123.208[.]170/images/scroll.png
• File description: Follow-up Trickbot EXE file, gtag lib43

TRAFFIC TO RETRIEVE THE INITIAL TRICKBOT BINARY (A DLL FILE):

• 98.142.109[.]186 port 80 - destinostumundo[.]com - GET /layout/recruter.php
• 98.142.109[.]186 port 443 (HTTPS) - destinostumundo[.]com - GET /layout/recruter.php

POST-INFECTION TRAFFIC FOR TRICKBOT:

• 108.170.20[.]72 port 443 - HTTPS traffic
• 179.191.108[.]58 port 449 - HTTPS traffic
• port 80 - checkip.amazonaws.com - GET /
• 177.87.0[.]7 port 447 - HTTPS traffic
• 103.102.220[.]50 port 443 - 103.102.220[.]50:443 - POST /rob13/[string with host and infection info]/81/
• 36.95.27[.]243 port 443 - 36.95.27[.]243:443 - POST /rob13/[string with host and infection info]/81/
• 103.102.220[.]50 port 443 - 103.102.220[.]50:443 - POST /rob13/[string with host and infection info]/83/
• 36.95.27[.]243 port 443 - 36.95.27[.]243:443 - POST /rob13/[string with host and infection info]/90

TRAFFIC CAUSED BY TRICKBOT'S PROPAGATION MODULES TO RETRIEVE ADDITIONAL TRICKBOT BINARIES (RETURNED EXE FILES):

• 195.123.208[.]170 port 80 - 195.123.208[.]170 - GET /images/control.png
• 195.123.208[.]170 port 80 - 195.123.208[.]170 - GET /images/scroll.png

ATTEMPTED TCP CONNECTIONS CAUSED BY THE INFECTED WINDOWS HOST:

• 45.14.226[.]115 port 443
• 169.239.45[.]42 port 449
• 92.242.214[.]203 port 449
• 94.158.245[.]54 port 443
• 38.132.99[.]174 port 80

Final words

A pcap of the infection traffic and the associated malware can be found here.

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