# MAR-10271944-1.v1 – North Korean Trojan: HOTCROISSANT

**us-cert.gov/ncas/analysis-reports/ar20-045d**

## Notification

This report is provided "as is" for informational purposes only. The Department of Homeland Security (DHS) does not provide any warranties of an
any information contained herein. The DHS does not endorse any commercial product or service referenced in this bulletin or otherwise.

This document is marked TLP:WHITE--Disclosure is not limited. Sources may use TLP:WHITE when information carries minimal or no foreseeab
accordance with applicable rules and procedures for public release. Subject to standard copyright rules, TLP:WHITE information may be distribute
For more information on the Traffic Light Protocol (TLP), see http://www.us-cert.gov/tlp.

## Summary

Description

This Malware Analysis Report (MAR) is the result of analytic efforts between Department of Homeland Security (DHS), the Federal Bureau of Inve
the Department of Defense (DoD). Working with U.S. Government partners, DHS, FBI, and DoD identified Trojan malware variants used by the N
government. This malware variant has been identified as HOTCROISSANT. The U.S. Government refers to malicious cyber activity by the North K
as HIDDEN COBRA. For more information on HIDDEN COBRA activity, visit https[:]//www[.]us-cert.gov/hiddencobra.

DHS, FBI, and DoD are distributing this MAR to enable network defense and reduce exposure to North Korean government malicious cyber activi

This MAR includes malware descriptions related to HIDDEN COBRA, suggested response actions and recommended mitigation techniques. Use
should flag activity associated with the malware and report the activity to the Cybersecurity and Infrastructure Security Agency (CISA) or the FBI C
(CyWatch), and give the activity the highest priority for enhanced mitigation.

This report looks at a full-featured beaconing implant. This sample performs a custom XOR network encoding and is capable of many features inc
system surveys, file upload/download, process and command execution, and performing screen captures.
[For a downloadable copy of IOCs, see MAR-10271944-1.v1.stix.](https://www.us-cert.gov/sites/default/files/publications/MAR-10271944-1.v1.stix.xml)

Submitted Files (1)

8ee7da59f68c691c9eca1ac70ff03155ed07808c7a66dee49886b51a59e00085 (svchost.exe)

IPs (1)

94.177.123.138

## Findings

**8ee7da59f68c691c9eca1ac70ff03155ed07808c7a66dee49886b51a59e00085**

Tags

trojan

Details

**Name** svchost.exe

**Size** 117760 bytes

**Type** PE32 executable (GUI) Intel 80386, for MS Windows

**MD5** 062e9cd9cdcabc928fc6186c3921e945

**SHA1** 566347f8bf30f66aec670d660091fb6bb03a0650

**SHA256** 8ee7da59f68c691c9eca1ac70ff03155ed07808c7a66dee49886b51a59e00085

**SHA512** e16fefb72fb466e31f982ea1d3f5e5754af289dfe7c8e7c2c6859b462b02e8715eaedf271985465931983fe0800f93e2943c715929f73136

**ssdeep** 3072:kRdlGZdOwoyeCJkLURXSOpW1yIR3vbRY7a:y3wMae2W9O+NR3DR0a

**Entropy** 6.282477

Antivirus

**Ahnlab** Trojan/Win32.Agent

**Avira** HEUR/AGEN.1039759

**BitDefender** Gen:Variant.Jaiko.2546

**Emsisoft** Gen:Variant.Jaiko.2546 (B)

**Ikarus** Trojan.Win32.KillAV


-----

**VirusBlokAda** BScope.Trojan.Tiggre

YARA Rules

rule CryptographyFunction

{
meta:
author = "CISA trusted 3rd party"

incident = "10271944.r1.v1"

date =  "2019-12-25"

category = "Hidden_Cobra"

family = "HOTCROISSANT"

strings:

$ALGO_crypto_1 = { 8A [1-5] 32 [1-4] 32 [1-4] 32 [1-4] 88 [1-5] 8A [1-4] 32 [1-4] 22 [1-4] 8B [1-5] 8D [3-7] 33 [1-4] 81 [3-7] C1 [1-5] C1 [
5] 33 [1-4] 22 [1-4] C1 [1-5] 33 [1-4] 32 [1-4] 8B [1-4] 83 [1-5] C1 [1-5] 33 [1-4] C1 [1-5] C1 }

condition:

uint16(0) == 0x5A4D and any of them

}

ssdeep Matches

No matches found.

PE Metadata

**Compile Date** 2019-07-25 11:38:54-04:00

**Import Hash** 9e7d183f56ad974fbd6c056d20051ef8

PE Sections

**MD5** **Name** **Raw Size** **Entropy**

760c39c49aa3a2cb4ec9f6fd5d4524e6 header 1024 2.537779

8480a50e20d57bcb86fa649691ca9e0c .text 80896 6.619532

36d3f909d39d54fd628e1d66d6acd26e .rdata 18432 5.282847

a497350b0c256c943b59382e0a2e884a .data 9216 2.905698

2d5b9737e8cd3def95c4fc6527741f91 .rsrc 1024 2.112640

9b5d24778302d0f050a93778c9cab3ef .reloc 7168 4.675041

Packers/Compilers/Cryptors

Microsoft Visual C++ ?.?

Description

The sample performs dynamic DLL importing and API lookups using LoadLibrary and GetProcAddress on obfuscated strings in an attempt to hide
network functions. However, only a small number of API calls are obfuscated this way, and their selection is not consistent through the sample.

The sample obfuscates strings used for API lookups as well as the strings used during the network handshake using a simple Byte xor with 0x0f.

The sample attempts to connect to a hardcoded C2 IP and then immediately sends it’s Victim Info. It then listens for commands from the C2 and r
Network communications are first zipped and then encoded with a custom xor algorithm. The session structure (Figure 1), packet format (Figure 2
(Figure 3), a Python 3 script to decrypt network traffic, and implant functionality (Figure 4) are given below.

--Begin Hardocoded IP and Port-
94.177.123.138:8088

--End Hardcoded IP and Port-
--Begin Python 3 Network Communication Decode Script-
def decode(data):

dec = []

key1 = 0x17

key2 = 0x00b8d68b

key3 = 0x02497029

for i in range(len(data)):

temp2 = key2

temp3 = key3

dec.append((data[i] ^ temp2 ^ temp3 ^ key1) & 0xff)

key2 = key2 >> 8 | ((((key2 * 8 ^ key2) & 0x7f8) << 0x14) & 0xffffffff)

k 1 k 1 & t 3 ^ (t 3 ^ k 1) & t 2


-----

y y | (((((((( y y ) ) ) y )
0xffffff80 ^ key3 << 7) & 0xffffffff) << 0x11) & 0xffffffff);
return bytes(dec)

--End Python 3 Network Communication Decode Script-Screenshots

**Figure 1 - Session Structure.**

**Figure 2 - Victim Information Structure.**

**Figure 3 - Implant Functionality. The following commands from the table above appear to be broken: ProcessKill - Programmer coding error that r**
violation. It attempts to decode an obfuscated string (Kernel32.dll) in-place instead of doing a string copy first like they do everywhere else. Windo
handle used to loop through all windows is never initialized.

**Figure 4 - Packet Structure.**

**94.177.123.138**

Tags

command-and-control

Ports


-----

Description

8EE7DA59F68C691C9ECA1AC70FF03155ED07808C7A66DEE49886B51A59E00085 connects to this C2 IP address.

## Recommendations

CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organizatio
configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.

Maintain up-to-date antivirus signatures and engines.
Keep operating system patches up-to-date.
Disable File and Printer sharing services. If these services are required, use strong passwords or Active Directory authentication.
Restrict users' ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators group unl
Enforce a strong password policy and implement regular password changes.
Exercise caution when opening e-mail attachments even if the attachment is expected and the sender appears to be known.
Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
Disable unnecessary services on agency workstations and servers.
Scan for and remove suspicious e-mail attachments; ensure the scanned attachment is its "true file type" (i.e., the extension matches the file
Monitor users' web browsing habits; restrict access to sites with unfavorable content.
Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs, etc.).
Scan all software downloaded from the Internet prior to executing.
Maintain situational awareness of the latest threats and implement appropriate Access Control Lists (ACLs).

Additional information on malware incident prevention and handling can be found in National Institute of Standards and Technology (NIST) Specia
**"Guide to Malware Incident Prevention & Handling for Desktops and Laptops".**

## Contact Information

CISA continuously strives to improve its products and services. You can help by answering a very short series of questions about this product at t
[https://us-cert.gov/forms/feedback/](https://us-cert.gov/forms/feedback/)

## Document FAQ

**What is a MIFR? A Malware Initial Findings Report (MIFR) is intended to provide organizations with malware analysis in a timely manner. In most**
report will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information
of desired analysis.

**What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manua**
engineering. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

**Can I edit this document? This document is not to be edited in any way by recipients. All comments or questions related to this document should**
[CISA at 1-888-282-0870 or soc@us-cert.gov.](http://10.10.0.46/mailto:soc@us-cert.gov)

**Can I submit malware to CISA? Malware samples can be submitted via three methods:**

Web: [https://malware.us-cert.gov](https://malware.us-cert.gov/)
E-Mail: [submit@malware.us-cert.gov](http://10.10.0.46/mailto:submit@malware.us-cert.gov)
FTP: ftp.malware.us-cert.gov (anonymous)

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and ph
[scams. Reporting forms can be found on CISA's homepage at www.us-cert.gov.](http://www.us-cert.gov/)

## Revisions

February 14, 2020: Initial Version

[This product is provided subject to this Notification and this](https://www.us-cert.gov/privacy/notification) [Privacy & Use policy.](https://www.dhs.gov/privacy-policy)

**Please share your thoughts.**

[We recently updated our anonymous product survey; we'd welcome your feedback.](https://www.surveymonkey.com/r/CISA-cyber-survey?product=https://us-cert.cisa.gov/ncas/analysis-reports/ar20-045d)


-----