ISC Stormcast For Wednesday, December 18th 2019 https://isc.sans.edu/podcastdetail.html?id=6794

Emotet infection with spambot activity

Published: 2019-12-18. Last Updated: 2019-12-18 00:03:30 UTC
by Brad Duncan (Version: 1)

Introduction

On Monday 2019-12-16, I tested some Emotet samples. I normally get Trickbot as the follow-up malware, which I've already documented from Monday. But every once in a while, I'll see spambot traffic instead of (or in addition to) Trickbot.

When I tested another Emotet sample later that day, I saw spambot traffic. Today's diary reviews information from that infection.

The email

On Monday afternoon (Unite States Central time), I saw an Emotet malspam message that made it to my inbox.

Shown above: Emotet malspam that made it to my inbox.

Why is the sender named Billy Idol? Because that was a name in the address book from one of my Emotet-infected Windows hosts a few months back. I generally make up names as I spin up vulnerable hosts in my lab. At some point, I vaguely remember using "Billy Idol" as a name when I'd set up a fake email account and generated some items for the inbox of a lab host.

That doesn't mean "Billy Idol" was infected. It just means an Emotet-infected host had an email in the inbox (or sent items) with an address using that name as an alias.

The email had an attached Word document, which I tested in my lab.

Shown above: Word doc from the email with macro for Emotet.

The infected Window host

My infected host had a Windows executable for Emotet made persistent through the Windows registry as shown below. This is normal behavior for Emotet.

Shown above: Emotet persistent on an infected Windows host.

Infection traffic

The traffic patterns were typical for Emotet. However, if an Emotet-infected Windows client turns into a spambot, it will generate SMTP and encrypted SMTP traffic. The spambot traffic is mostly encrypted SMTP--in fact, most often all of it is encrypted. But sometimes you might find unencrypted SMTP when reviewing the traffic in Wireshark as shown below. You can also use Wireshark to export emails found in unencrypted SMTP traffic from the pcap.

Shown above: Filtering on web traffic in Wireshark shows SSL/TLS spambot traffic to mailservers, mostly over TCP ports 25, 465, and 587.

Shown above: You can filter on various SMTP commands (like EHLO) to get a better idea of the encrypted/unencrypted spambot traffic.

Shown above: You can filter on smtp.data.fragment to find any emails in the pcap from unencrypted SMTP.

Shown above: Using Wireshark to export emails from unencrypted email traffic in a pcap.

Shown above: Traffic from my infected lab host only had one email I could export from the pcap.

Shown above: The exported email file opened in a text editor.

Indicators of Compromise (IoCs)

Malware from an infected Windows host:

SHA256 hash: b82542fa69e2a8936972242c0d2d5049235b6b0d24030073a886937f1f179680

File size: 191,744 bytes
File name: INVOICE.doc
File description: Malspam attachment--Word doc with macro for Emotet

SHA256 hash: 8bfb28788bd813e2ec3e7dc0cce9c95bda8d5df89a65b911c539e0a6aebcfc05

File size: 307,528 bytes
File location: hxxp://blog.itsaboutnature[.]net/confabulate-grainy/tad0m4bjt-li6lr-5546823/
File location: C:\Users\[username]\26.exe
File location: C:\Users\[username]\AppData\local\iascors\iascors.exe
File description: Emotet malware binary retrieved by Word macro

Traffic caused by Word macro to retrieve an Emotet EXE file:

104.27.149[.]107 port 80 - www.simple-it[.]org - attempted TCP connections but no response from the server
43.255.154[.]108 port 443 - www.uaeneeds[.]com - HTTPS/SSL/TLS traffic
157.7.106[.]97 port 80 - oki-dental[.]com - GET /sys/upydu-4nmmykhbf-292/
65.254.248[.]88 port 80 - blog.itsaboutnature[.]net - GET /confabulate-grainy/tad0m4bjt-li6lr-5546823/

Emotet post-infection HTTP traffic:

190.38.252[.]45 port 443 - 190.38.252[.]45:443 - POST /Zm3bDTIjDcE0VBqqFO
105.225.77[.]21 port 80 - 105.225.77[.]21 - POST /7rS6p32cGJz6yHNBUKW
181.167.35[.]84 port 80 - 181.167.35[.]84 - POST /Utmt2SR
164.68.115[.]146 port 8080 - 164.68.115[.]146:8080 - POST /dzbBGrkIdBkIqwPjf
5.189.148[.]98 port 8080 - 5.189.148[.]98:8080 - POST /DmiI74YHj
5.189.148[.]98 port 8080 - 5.189.148[.]98:8080 - POST /lmmBjn
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /lmmBjn
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /QIrnjidOBG
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /fsIL1F4aeW
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /Qb6Hb0ONYVQ2an
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /Cux8Ia00axEqkIhB2
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /lqcZ9GHhKIkoVPdb
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /xaMc6JN
64.207.176[.]141 port 8080 - 64.207.176[.]141:8080 - POST /VJ9ZrKRKSWYOwNrPCk
82.145.43[.]153 port 8080 - 82.145.43[.]153:8080 - POST /PKgFIQr2tR
149.202.153[.]251 port 8080 - 149.202.153[.]251:8080 - POST /iEo555d
149.202.153[.]251 port 8080 - 149.202.153[.]251:8080 - POST /1SxH7