Analysis Report

MAR-10265965-2.v1 – North Korean Trojan: SLICKSHOES

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Alert Code


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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 SLICKSHOES. 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[.]

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 sample is a Themida-packed dropper that decodes and drops a file "C:\Windows\Web\taskenc.exe" which is a Themida-packed beaconing implant. The beaconing implant does not execute the dropped file nor does it schedule any tasks to run the malware. The dropped beaconing implant uses an indigenous network encoding algorithm and is capable of many features including conducting system surveys, file upload/download, process and command execution, and screen captures.

For a downloadable copy of IOCs, see MAR-10265965-2.v1.stix.

Submitted Files (1)

fdb87add07d3459c43cfa88744656f6c00effa6b7ec92cb7c8b911d233aeb4ac (CCA9FBB11C194FC53015185B741887...)

IPs (1)





Name CCA9FBB11C194FC53015185B741887A8
Size 3133440 bytes
Type PE32 executable (GUI) Intel 80386, for MS Windows
MD5 cca9fbb11c194fc53015185b741887a8
SHA1 9e7bf03a607558dafe146907db28d77fda81be22
SHA256 fdb87add07d3459c43cfa88744656f6c00effa6b7ec92cb7c8b911d233aeb4ac
SHA512 a1d1747dbc96c14b45f345679c0f7ba38186458f4992eecf382dd0af6391b4224c1b487431d681f5ffd052839f2901bc6203ea81c3235efcd82061d60eb10618
ssdeep 49152:bbcROoCHuumCvGyQwNr6Ljvhg1J/4fxcBhmdSP8sWNRy8kLn3o1Dn:jVHaaGyQG6npcJ4xcD5d2Ry8kDo
Entropy 7.968879
Ahnlab Trojan/Win32.Agent
Antiy Trojan/Win32.Casdet
Avira TR/Crypt.TPM.Gen
BitDefender Gen:Variant.Barys.1619
ClamAV Win.Trojan.Agent-7376504-0
Cyren W32/Trojan.QBAU-3559
ESET a variant of Win32/Packed.Themida.AOO trojan
Emsisoft Gen:Variant.Barys.1619 (B)
Ikarus Trojan.Win32.Themida
K7 Trojan ( 0040f4ef1 )
McAfee Trojan-Themida
Microsoft Security Essentials Trojan:Win32/Emotet
NANOAV Trojan.Win32.TPM.ggaakh
Sophos Troj/Agent-BCXR
Symantec Trojan Horse
VirusBlokAda Trojan.Wacatac
Zillya! Trojan.Themida.Win32.3185
YARA Rules

No matches found.

ssdeep Matches

No matches found.

PE Metadata
Compile Date 2018-02-26 20:08:54-05:00
Import Hash baa93d47220682c04d92f7797d9224ce
PE Sections
MD5 Name Raw Size Entropy
0de0ceb73fba415dc20a730f628429a6 header 4096 0.816628
74520bd2f6bb3211bd82b6f9547ff207   1572864 7.979303
32762b0a8ae1347aebaba811505cadcf .rsrc 49152 4.290489
79cf217f58f3178dafbfe532c01ef5c4 .idata 512 1.308723
f0347e7e1ac9efb817c55b3ba9e5bf2d   512 0.264678
4fb94c6713c62a51c1b230a2bc033fac suylcrzz 1505792 7.954736
81610ae95a418f6ef9ef042b37a26c4a ajqluhke 512 3.110274
fdb87add07... Connected_To

This sample is a Themida-packed dropper that decodes and drops an embedded file (MD5: B57DB76CC1C0175C4F18EA059D9E2AB2 / SHA256: 7250ccf4fad4d83d087a03d0dd67d1c00bf6cb8e7fa718140507a9d5ffa50b54) to C:\Windows\Web\taskenc.exe. This dropper does not execute the dropped file or create any auto-run keys or scheduled tasks to execute it.

The dropped file (taskenc.exe) is a Themida-packed beaconing implant with RAT functionality. The implant beacons to a hardcoded IP ( over the hardcoded TCP port 80 every 60 seconds. The initial beacon contains the string “ApolloZeus” as well as victim information, including OS version, user name, and IP address. All traffic, including the beacon, is encoded with an indigenous encoding algorithm. Due to the way the implant decodes the hardcoded string “ApolloZeus” in-place in memory, the first beacon contains the string in plaintext, the second beacon will contain the string encoded, and so on. This is probably unintended and an oversight by the developers.

--Begin Packet Format--
[8 Bytes data length][2Byte Opcode][data]
--End Packet Format--

--Begin Victim Information--
OS Version
User name
IP address
--End Victim Information--

A Python3 script for decoding the traffic is displayed below:

--Begin Python3 Script--
def decode(enc):
dec = b’’
key1 = 0x49;
key2 = 0x1310a024;
key3 = 0xa323da32;

for e in enc:
   dec += chr((ord(e) ^ key3 ^ key1) & 0xff)
   tmp1 = key3 >> 8
   key1 = (key2>>0x10) & (key2>>8) & key2 ^ (key3>>0x10) & tmp1 ^ key3 & key1 ^ (key3>>0x18);
   tmp2 = key3 * 2 ^ key3;
   key3 = key2 << 0x18 | key3 >> 8;
   key2 = (tmp2 & 0x1fe) << 0x16 | key2 >> 8;
return dec
--End Python3 Script--


Figure 1 - Implant Functionality.

Figure 1 - Implant Functionality.

  • 80 TCP
Relationships Connected_From fdb87add07d3459c43cfa88744656f6c00effa6b7ec92cb7c8b911d233aeb4ac

Hardcoded C2 address used in implant.

Relationship Summary

fdb87add07... Connected_To Connected_From fdb87add07d3459c43cfa88744656f6c00effa6b7ec92cb7c8b911d233aeb4ac


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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February 14, 2020: Initial Version