Introduction

This week, we've seen IcedID (Bokbot) distributed through thread-hijacked emails with PDF attachments.  The PDF files have links that redirect to Google Firebase Storage URLs hosting password-protected zip archives.  The password for the downloaded zip archive is shown in the PDF file.  The downloaded zip archives contain EXE files that are digitally-signed using a certificate issued by SSL.com.  The EXE file is designed to install IcedID malware on a vulnerable Windows host.

Today's diary reviews an IcedID infection generated on Tuesday 2023-04-11.

Shown above:  Chain of events for IcedID infections so far this week.

Images from the infection

Shown above:  Example of thread-hijacked email pushing IcedID from Tuesday 2023-04-11.

Shown above:  Attached to the email, this PDF file has a link to download a password-protected zip archive.

Shown above:  EXE extracted from the zip archive is digitally signed using a certificate issued by SSL.com.

Shown above:  Scheduled task to keep the IcedID infection persistent.

Shown above:  Persistent DLL for IcedID and the data binary used to run the persistent DLL.

Shown above:  Traffic from the infection filtered in Wireshark.

Files From an Infected Windows Host

SHA256 hash: 6d07c2e05e76dd17f1871c206e92f08b69c5a7804d646e5f1e943a169a8c50ee

• File size: 27,273 bytes
• File name: INV_Unpaid_683_April.pdf
• File description: PDF file attached to thread-hijacked email distributing IcedID

SHA256 hash: 59e0f6e9c4ce2ab8116049d59525c6391598f2def4125515d86b61822926784f

• File size: 58,031 bytes
• File name: Docs_Inv_April_11_450.zip
• File location: hxxps://firebasestorage.googleapis[.]com/v0/b/logical-waters-377622.appspot.com/o/MCRERY0iJA%2FDocs_Inv_April_11_450.zip?alt=media&token=799ca8a7-44ce-44e8-b93d-a346faaf0ea3
• File description: password-protected zip archive downloaded from link in above PDF file
• Password: 572

SHA256 hash: 52d3dd78d3f1a14e18d0689ed8c5b43372f9e76401ef1ff68522575e6251d2cf

• File size: 131,168 bytes
• File name: Docs_Inv_April_11_450.exe
• File description: Extracted from the above zip archive, a 64-bit, digitally-signed EXE to install IcedID

SHA256 hash: 54d064799115f302a66220b3d0920c1158608a5ba76277666c4ac532b53e855f

• File size: 647,389 bytes
• File description: Gzip binary from shoterqana[.]com retreived by above EXE

SHA256 hash: dbf233743eb74ab66af8d1c803f53b7fe313ed70756efcc795ea4082c2f3c0c8

• File size: 354,282 bytes
• File location: C:\Users\[username]\AppData\Roaming\[random directory name]\license.dat
• File description: data binary used to run persistent IcedID DLL

SHA256 hash: 5953f8f23092714626427316dd66ff2e160f03d2c57dcb1a4745d2e593c907ae

• File size: 292,352 bytes
• File location: C:\Users\[username]\AppData\[random directory path under Local or Roaming]\[random name].dll
• File description: Persistent IcedID DLL (64-bit DLL)
• Run method: rundll32.exe [file name],init --ashego="[path to license.dat]"

Traffic From an Infected Windows Host

Link from the PDF file:

• hxxp://80.77.23[.]51/lndex.php

Above URL redirected to:

• hxxps://firebasestorage.googleapis[.]com/v0/b/logical-waters-377622.appspot.com/o/MCRERY0iJA%2FDocs_Inv_April_11_450.zip?alt=media&token=799ca8a7-44ce-44e8-b93d-a346faaf0ea3

Caused when running the extracted EXE, because the EXE was digitally signed using a certificate from SSL.com:

• hxxp://www.ssl[.]com/repository/SSLcom-RootCA-EV-RSA-4096-R2.crt
• Note: The above URL is not malicious, but it's an indicator for this particular infection chain.

Installer EXE for IcedID retrieves gzip binary:

• 172.86.75[.]64 port 80 - shoterqana[.]com - GET / HTTP/1.1

IcedID C2:

• 192.153.57[.]82 port 443 - villageskaier[.]com - HTTPS traffic
• 162.33.178[.]40 port 443 - deadwinston[.]com - HTTPS traffic

Final words

Running recent IcedID samples in a lab environment this week generated IcedID BackConnect traffic over 45.61.137[.]159 over TCP port 443 (reference) and 193.149.176[.]100, also using TCP port 443 (reference).  443 is a new TCP port for IcedID BackConnect traffic, which previously used TCP port 8080.  These two IP addresses are good indicators of an on-going IcedID infection if you find traffic to these servers from your network.

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