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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[.]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 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)
||PE32 executable (GUI) Intel 80386, for MS Windows
||a variant of Win32/Packed.Themida.AOO trojan
||Trojan ( 0040f4ef1 )
|Microsoft Security Essentials
No matches found.
No matches found.
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 (220.127.116.11) 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--
--End Victim Information--
A Python3 script for decoding the traffic is displayed below:
--Begin Python3 Script--
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;
--End Python3 Script--
Figure 1 - Implant Functionality.
Hardcoded C2 address used in implant.
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".
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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.
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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.