Malware Analysis Report (AR20-045D)

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

Notification

This report is provided "as is" for informational purposes only. The Department of Homeland Security (DHS) does not provide any warranties of any kind regarding 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 foreseeable risk of misuse, in accordance with applicable rules and procedures for public release. Subject to standard copyright rules, TLP:WHITE information may be distributed without restriction. 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 Investigation (FBI), and the Department of Defense (DoD). Working with U.S. Government partners, DHS, FBI, and DoD identified Trojan malware variants used by the North Korean government. This malware variant has been identified as HOTCROISSANT. The U.S. Government refers to malicious cyber activity by the North Korean government 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 activity.

This MAR includes malware descriptions related to HIDDEN COBRA, suggested response actions and recommended mitigation techniques. Users or administrators should flag activity associated with the malware and report the activity to the Cybersecurity and Infrastructure Security Agency (CISA) or the FBI Cyber Watch (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 including conducting 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.

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 e16fefb72fb466e31f982ea1d3f5e5754af289dfe7c8e7c2c6859b462b02e8715eaedf271985465931983fe0800f93e2943c715929f731368ca81deb5ddf3b54
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 [1-5] 0B [1-4] 8D [1-5] 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 it’s usage of 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 returns the results. Network communications are first zipped and then encoded with a custom xor algorithm. The session structure (Figure 1), packet format (Figure 2), victim information (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)
       key1 = key1 & temp3 ^ (temp3 ^ key1) & temp2
       key3 = key3 >> 8 | ((((((((key3 * 2 ^ key3) << 4) & 0xffffffff) ^ key3) &
               0xffffff80 ^ key3 << 7) & 0xffffffff) << 0x11) & 0xffffffff);
   return bytes(dec)

--End Python 3 Network Communication Decode Script--

Screenshots
Figure 1 - Session Structure.

Figure 1 - Session Structure.

Figure 2 - Victim Information 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 results in an access violation. It attempts to decode an obfuscated string (Kernel32.dll) in-place instead of doing a string copy first like they do everywhere else. WindowClose - The handle used to loop through all windows is never initialized.

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

Figure 4 - Packet Structure.

Figure 4 - Packet Structure.

94.177.123.138

Tags

command-and-control

Ports
  • 8088 TCP
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 organization's systems. Any 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 unless required.
  • 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 header).
  • 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) Special Publication 800-83, "Guide to Malware Incident Prevention & Handling for Desktops and Laptops".

Contact Information

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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 instances this report will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.

What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manual reverse 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 be directed to the CISA at 1-888-282-0870 or soc@us-cert.gov.

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

CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and phishing-related scams. Reporting forms can be found on CISA's homepage at www.us-cert.gov.

Revisions

February 14, 2020: Initial Version

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