North Korea’s DDoS Botnet Infrastructure

This joint Technical Alert (TA) is the result of analytic efforts between the Department of Homeland Security (DHS) and the Federal Bureau of Investigation (FBI). This alert provides technical details on the tools and infrastructure used by cyber actors of the North Korean government to target the media, aerospace, financial, and critical infrastructure sectors in the United States and globally. Working with U.S. Government partners, DHS and FBI identified Internet Protocol (IP) addresses associated with a malware variant, known as DeltaCharlie, used to manage North Korea’s distributed denial-of-service (DDoS) botnet infrastructure. This alert contains indicators of compromise (IOCs), malware descriptions, network signatures, and host-based rules to help network defenders detect activity conducted by the North Korean government. The U.S. Government refers to the malicious cyber activity by the North Korean government as HIDDEN COBRA.

If users or administrators detect the custom tools indicative of HIDDEN COBRA, these tools should be immediately flagged, reported to the DHS National Cybersecurity Communications and Integration Center (NCCIC) or the FBI Cyber Watch (CyWatch), and given highest priority for enhanced mitigation. This alert identifies IP addresses linked to systems infected with DeltaCharlie malware and provides descriptions of the malware and associated malware signatures. DHS and FBI are distributing these IP addresses to enable network defense activities and reduce exposure to the DDoS command-and-control network. FBI has high confidence that HIDDEN COBRA actors are using the IP addresses for further network exploitation.

This alert includes technical indicators related to specific North Korean government cyber operations and provides suggested response actions to those indicators, recommended mitigation techniques, and information on reporting incidents to the U.S. Government.

Description
Since 2009, HIDDEN COBRA actors have leveraged their capabilities to target and compromise a range of victims; some intrusions have resulted in the exfiltration of data while others have been disruptive in nature. Commercial reporting has referred to this activity as Lazarus Group[1] (link is external) and Guardians of Peace.[2] (link is external) DHS and FBI assess that HIDDEN COBRA actors will continue to use cyber operations to advance their government’s military and strategic objectives. Cyber analysts are encouraged to review the information provided in this alert to detect signs of malicious network activity.

Tools and capabilities used by HIDDEN COBRA actors include DDoS botnets, keyloggers, remote access tools (RATs), and wiper malware. Variants of malware and tools used by HIDDEN COBRA actors include Destover,[3] (link is external) Wild Positron/Duuzer,[4] (link is external) and Hangman.[5] (link is external) DHS has previously released Alert TA14-353A,[6] which contains additional details on the use of a server message block (SMB) worm tool employed by these actors. Further research is needed to understand the full breadth of this group’s cyber capabilities. In particular, DHS recommends that more research should be conducted on the North Korean cyber activity that has been reported by cybersecurity and threat research firms.

HIDDEN COBRA actors commonly target systems running older, unsupported versions of Microsoft operating systems. The multiple vulnerabilities in these older systems provide cyber actors many targets for exploitation. These actors have also used Adobe Flash player vulnerabilities to gain initial entry into users’ environments.

HIDDEN COBRA is known to use vulnerabilities affecting various applications. These vulnerabilities include:

• CVE-2015-6585: Hangul Word Processor Vulnerability
• CVE-2015-8651: Adobe Flash Player 18.0.0.324 and 19.x Vulnerability
• CVE-2016-0034: Microsoft Silverlight 5.1.41212.0 Vulnerability
• CVE-2016-1019: Adobe Flash Player 21.0.0.197 Vulnerability
• CVE-2016-4117: Adobe Flash Player 21.0.0.226 Vulnerability

We recommend that organizations upgrade these applications to the latest version and patch level. If Adobe Flash or Microsoft Silverlight is no longer required, we recommend that those applications be removed from systems.

The indicators provided with this alert include IP addresses determined to be part of the HIDDEN COBRA botnet infrastructure, identified as DeltaCharlie. The DeltaCharlie DDoS bot was originally reported by Novetta in their 2016 Operation Blockbuster Malware Report.[7] (link is external) This malware has used the IP addresses identified in the accompanying .csv and .stix files as both source and destination IPs. In some instances, the malware may have been present on victims’ networks for a significant period.

Technical Details
DeltaCharlie is a DDoS tool used by HIDDEN COBRA actors, and is referenced and detailed in Novetta’s Operation Blockbuster Destructive Malware report. The information related to DeltaCharlie from the Operation Blockbuster Destructive Malware report should be viewed in conjunction with the IP addresses listed in the .csv and .stix files provided within this alert. DeltaCharlie is a DDoS tool capable of launching Domain Name System (DNS) attacks, Network Time Protocol (NTP) attacks, and Character Generation Protocol attacks. The malware operates on victims’ systems as a svchost-based service and is capable of downloading executables, changing its own configuration, updating its own binaries, terminating its own processes, and activating and terminating denial-of-service attacks. Further details on the malware can be found in Novetta’s report.

Detection and Response
HIDDEN COBRA IOCs related to DeltaCharlie are provided within the accompanying .csv and .stix files of this alert. DHS and FBI recommend that network administrators review the IP addresses, file hashes, network signatures, and YARA rules provided, and add the IPs to their watchlist to determine whether malicious activity has been observed within their organization.

When reviewing network perimeter logs for the IP addresses, organizations may find numerous instances of these IP addresses attempting to connect to their systems. Upon reviewing the traffic from these IP addresses, system owners may find that some traffic corresponds to malicious activity and some to legitimate activity. System owners are also advised to run the YARA tool on any system they suspect to have been targeted by HIDDEN COBRA actors. Additionally, the appendices of this report provide network signatures to aid in the detection and mitigation of HIDDEN COBRA activity.

Network Signatures and Host-Based Rules
This section contains network signatures and host-based rules that can be used to detect malicious activity associated with HIDDEN COBRA actors. Although created using a comprehensive vetting process, the possibility of false positives always remains. These signatures and rules should be used to supplement analysis and should not be used as a sole source of attributing this activity to HIDDEN COBRA actors.

Network Signatures

alert tcp any any -> any any (msg:”DPRK_HIDDEN_COBRA_DDoS_HANDSHAKE_SUCCESS”; dsize:6; flow:established,to_server; content:”|18 17 e9 e9 e9 e9|”; fast_pattern:only; sid:1; rev:1;)

Source: https://www.us-cert.gov/ncas/alerts/TA17-164A

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