TA551: Email Attack Campaign Switches from Valak to IcedID

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January 7, 2021 at 12:01 AM

Tags: IcedID, Shathak, TA551, Ursnif, Valak

The image represents malicious email campaigns, such as TA551, often push a variety of malware, such as Valak and IcedID.

This post is also available in: 日本語 (Japanese)

Executive Summary

TA551 (also known as Shathak) is an email-based malware distribution campaign that often targets English-speaking victims. The campaign discussed in this blog has targeted German, Italian and Japanese speakers. TA551 has historically pushed different families of information-stealing malware like Ursnif and Valak. After mid-July 2020, this campaign has exclusively pushed IcedID malware, another information stealer.

This blog provides an overview of TA551, as well as previous activity from this campaign. We also examine changes from this campaign since our previous blog about TA551 pushing Valak in July 2020.

Palo Alto Networks Next-Generation Firewall customers are protected from this threat with the Threat Prevention security subscription, which detects the malware. AutoFocus customers can track this activity using the TA551 and IcedID tags.

Infection Chain of Events

From mid-July through November 2020, TA551 has remained consistent in its infection process. A flow chart for the chain of events is shown in Figure 1.

TA551 (Shathak) chain of events include 1) malicious email with attachment, 2) attached zip archive, password-protected, 3) extracted Word document, 4) enable macros, 5) HTTP traffic for IcedID installer, 6) installer DLL, 7) HTTPS traffic for IcedID binary, 8) IcedID binary persistent on the infected host, 9) HTTPS post-infection traffic. — Figure 1. Chain of events for TA551 (Shathak) from July through November 2020.

The initial lure is an email spoofing an email chain. These email chains are retrieved from email clients on previously infected hosts. The message has an attached ZIP archive and a message informing the user of a password necessary to open the attachment.

After opening the ZIP archive, the victim finds a Microsoft Word document with macros. If the victim enables macros on a vulnerable Windows computer, the victim’s host retrieves an installer DLL for IcedID malware. This will infect a vulnerable Windows computer. See FIgures 2-7 for a recent example targeting a Japanese-speaking victim.

A malicious email targeting a Japanese-speaking victim on Nov. 4, 2020, including a ZIP archive that leads to an installer DLL for IcedID malware. — Figure 2. An example of TA551 email targeting a Japanese-speaking victim on Nov. 4, 2020.

The screenshot shows a user opening the ZIP archive using the password provided in the malicious email. — Figure 3. Using password from the message to open the ZIP archive.

The Word document retrieved from the malicious ZIP archive contains macros which can harm a vulnerable computer if enabled. — Figure 4. Screenshot of Word document from the ZIP archive.

The screenshot shows traffic from an IcedID infection filtered in Wireshark. — Figure 5. Traffic from an infection filtered in Wireshark.

Files and directories created during the infection process on a Windows host include the inital IcedID DLL, installer DLL, copy of mshta.exe and persistent IcedID DLL. These files and directories are indicated with red arrows in the screenshot. — Figure 6. Files and directories created during the infection process on a Windows host.

The screenshot shows a scheduled task with "multiple triggers defined." This task keeps the IcedID infection persistent on an infected Windows host. — Figure 7. Scheduled task to keep the IcedID infection persistent on an infected Windows host.

TA551 Switches to IcedID

We have a GitHub repository where we track recent TA551 activity. The repository contains information on each wave of attack from TA551 since July 6, 2020. Starting on July 14, 2020, we have only seen IcedID malware from these waves of attack.

Since July 14, 2020, these waves of malspam consistently targeted English-speaking victims until Oct. 27, 2020, when we started seeing Japanese templates for the Word documents. TA551 consistently targeted Japanese-speaking victims from Oct. 27-Nov. 20, 2020. After approximately three weeks of Japanese-focused attacks, TA551 switched back to English-speaking victims starting on Nov. 24, 2020.

Regardless of the targeted group, TA551 continues to push IcedID as its malware payload.

History of TA551

We have traced TA551 as far back as February 2019, and since that time, we have noted the following characteristics:

TA551 has distributed different families of malware, including Ursnif (Gozi/ISFB), Valak and IcedID.
TA551 malspam spoofs legitimate email chains based on data retrieved from previously infected Windows hosts. It sends copies of these email chains to recipients of the original email chain.
The spoofed email includes a short message as the most recent item in the chain. This is a generic statement asking the recipient to open an attached ZIP archive using the supplied password.
File names for the ZIP archives use the name of the company being spoofed in the email. For example, if the spoofed sender is someone@companyname.com, the ZIP attachment would be named companyname.zip.
In 2020, we also started seeing emails with info.zip or request.zip as the attached ZIP archive names.
These password-protected ZIP attachments contain a Word document with macros to install malware.
File names for the extracted Word documents follow noticeable patterns that have evolved as this campaign has progressed.
URLs generated by the associated Word macros also follow noticeable patterns that have also evolved as this campaign has progressed.

TA551 in 2019

Figure 8 shows the earliest email we can confirm from this campaign, dated Feb. 4, 2019. It targeted an English-speaking recipient and pushed Ursnif malware.