MAR-10288834-3.v1 – North Korean Trojan: PEBBLEDASH
NotificationThis 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. SummaryDescriptionThis Malware Analysis Report (MAR) is the result of analytic efforts between the 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 PEBBLEDASH. 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. FBI has high confidence that HIDDEN COBRA actors are using malware variants in conjunction with proxy servers to maintain a presence on victim networks and to further network exploitation. 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 uses FakeTLS for session authentication and for network encoding utilizing RC4. It has the capability to download, upload, delete, and execute files; enable Windows CLI access; create and terminate processes; and perform target system enumeration. For a downloadable copy of IOCs, see MAR-10288834-3.v1.stix. Submitted Files (1)aab2868a6ebc6bdee5bd12104191db9fc1950b30bcf96eab99801624651e77b6 (D2DE01858417FA3B580B3A95857847...) IPs (1)112.217.108.138 Findingsaab2868a6ebc6bdee5bd12104191db9fc1950b30bcf96eab99801624651e77b6Tagsrootkittrojan Details
Antivirus
YARA Rules
ssdeep Matches
PE Metadata
PE Sections
Packers/Compilers/Cryptors
Relationships
DescriptionThe sample performs dynamic dynamic link library (DLL) importing and application programming interface (API) lookups using LoadLibrary and GetProcAddress on obfuscated strings in an attempt to hide it’s usage of network functions. The sample obfuscates strings used for API lookups using a custom XOR algorithm. A Python3 script to decrypt the obfuscated strings is given below. --Begin Python3 script-- dec += bytes([enc[i] ^ key[15]]) The sample obfuscates its callback descriptors (IP address and ports) using a different custom XOR algorithm. A Python3 script to decrypt the obfuscated data is given below. --Begin Python3 script-- The sample utilizes a “FakeTLS” scheme in an attempt to obfuscate its network communications. It picks a random Uniform Resource Locator (URL) from a list (Figure 1) to use in the TLS certificate. The sample and the command and control (C2) externally appear to perform a standard TLS authentication, however, most of the fields used are filled with random data from rand(). --Begin C2-- Once the FakeTLS handshake is complete, all further packets use a FakeTLS header, followed by RC4 encrypted data. --Begin packet structure-- The sample then waits for commands from the C2. Screenshots Figure 1 - List of certificate URLs used in the TLS certificate. Figure 2 - The implant contains the commands displayed in the table. 112.217.108.138Tagscommand-and-control Relationships
DescriptionThe malware attempts to connect to the IP address. Relationship Summary
MitigationThe following Snort rule can be used to detect the FakeTLS RC4 encrypted command packets: //Detects the FakeTLS RC4 encrypted command packets alert tcp any any -> any any (msg:"Malware Detected"; pcre:" /\x17\x03\x01\x00\x08.\x20\x59\x2c/"; rev:1; sid:99999999;) RecommendationsCISA 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.
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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Revisions
May 12, 2020: Initial Version
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