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Actions to take today:
• Install fixed builds, updating all affected VMware Horizon and UAG systems to the latest versions. If updates or workarounds were not promptly applied following VMware’s release of updates for Log4Shell in December 2021, treat all affected VMware systems as compromised.
• Minimize the internet-facing attack surface by hosting essential services on a segregated demilitarized (DMZ) zone, ensuring strict network perimeter access controls, and implementing regularly updated web application firewalls (WAFs) in front of public-facing services
The Cybersecurity and Infrastructure Security Agency (CISA) and United States Coast Guard Cyber Command (CGCYBER) are releasing this joint Cybersecurity Advisory (CSA) to warn network defenders that cyber threat actors, including state-sponsored advanced persistent threat (APT) actors, have continued to exploit CVE-2021-44228 (Log4Shell) in VMware Horizon® and Unified Access Gateway (UAG) servers to obtain initial access to organizations that did not apply available patches or workarounds.
Since December 2021, multiple threat actor groups have exploited Log4Shell on unpatched, public-facing VMware Horizon and UAG servers. As part of this exploitation, suspected APT actors implanted loader malware on compromised systems with embedded executables enabling remote command and control (C2). In one confirmed compromise, these APT actors were able to move laterally inside the network, gain access to a disaster recovery network, and collect and exfiltrate sensitive data.
This CSA provides the suspected APT actors’ tactics, techniques, and procedures (TTPs), information on the loader malware, and indicators of compromise (IOCs). The information is derived from two related incident response engagements and malware analysis of samples discovered on the victims’ networks.
CISA and CGCYBER recommend all organizations with affected systems that did not immediately apply available patches or workarounds to assume compromise and initiate threat hunting activities using the IOCs provided in this CSA, Malware Analysis Report MAR-10382580-1, and MAR-10382254-1. If potential compromise is detected, administrators should apply the incident response recommendations included in this CSA and report key findings to CISA.
Update July 18, 2022:
This Cybersecurity Advisory (CSA) has been updated with additional Malware Analysis Report MAR-10382580-2, which provides additional indicators of compromise (IOCs).
Update End
See the list below to download copies of IOCs:
Download the pdf version of this report: [pdf, 426 kb]
Note: this advisory uses the MITRE ATT&CK for Enterprise framework, version 11. See Appendix A for a table of the threat actors’ activity mapped to MITRE ATT&CK® tactics and techniques.
Log4Shell is a remote code execution vulnerability affecting the Apache® Log4j library and a variety of products using Log4j, such as consumer and enterprise services, websites, applications, and other products, including certain versions of VMware Horizon and UAG. The vulnerability enables malicious cyber actors to submit a specially crafted request to a vulnerable system, causing the system to execute arbitrary code. The request allows the malicious actors to take full control of the affected system. (For more information on Log4Shell, see CISA’s Apache Log4j Vulnerability Guidance webpage and VMware advisory VMSA-2021-0028.13.)
VMware made fixes available in December 2021 and confirmed exploitation in the wild on December 10, 2021.[1] Since December 2021, multiple cyber threat actor groups have exploited [T1190] Log4Shell on unpatched, public-facing VMware Horizon and UAG servers to obtain initial access [TA0001] to networks.
After obtaining access, some actors implanted loader malware on compromised systems with embedded executables enabling remote C2. These actors connected to known malicious IP address 104.223.34[.]198.[2] This IP address uses a self-signed certificate CN: WIN-P9NRMH5G6M8. In at least one confirmed compromise, the actors collected and exfiltrated sensitive information from the victim’s network.
The sections below provide information CISA and CGCYBER obtained during incident response activities at two related confirmed compromises.
CGCYBER conducted a proactive threat-hunting engagement at an organization (Victim 1) compromised by actors exploiting Log4Shell in VMware Horizon. After obtaining access, threat actors uploaded malware, hmsvc.exe, to a compromised system. During malware installation, connections to IP address 104.223.34[.]198 were observed.
CISA and CGCYBER analyzed a sample of hmsvc.exe from the confirmed compromise. hmsvc.exe masquerades as a legitimate Microsoft® Windows® service (SysInternals LogonSessions software) [T1036.004] and appears to be a modified version of SysInternals LogonSessions software embedded with malicious packed code. When discovered, the analyzed sample of hmsvc.exe was running as NT AUTHORITYSYSTEM, the highest privilege level on a Windows system. It is unknown how the actors elevated privileges. hmsvc.exe is a Windows loader containing an embedded executable, 658_dump_64.exe. The embedded executable is a remote access tool that provides an array of C2 capabilities, including the ability to log keystrokes [T1056.001], upload and execute additional payloads [T1105], and provide graphical user interface (GUI) access over a target Windows system’s desktop. The malware can function as a C2 tunneling proxy [T1090], allowing a remote operator to pivot to other systems and move further into a network.
When first executed, hmsvc.exe creates the Scheduled Task [T1053.005], C:WindowsSystem32TasksLocal Session Updater, which executes malware every hour. When executed, two randomly named *.tmp files are written to the disk at the location C:Users<USER>AppDataLocalTemp and the embedded executable attempts to connect to hard-coded C2 server 192.95.20[.]8 over port 4443, a non-standard port [TT571]. The executable’s inbound and outbound communications are encrypted with a 128-bit key [T1573.001].
For more information on hmsvc.exe, including IOCs and detection signatures, see MAR-10382254-1.
From late April through May 2022, CISA conducted an onsite incident response engagement at an organization (Victim 2) where CISA observed bi-directional traffic between the organization and suspected APT IP address 104.223.34[.]198. During incident response, CISA determined Victim 2 was compromised by multiple threat actor groups.
The threat actors using IP 104.223.34[.]198 gained initial access to Victim 2’s production environment in late January 2022, or earlier. These actors likely obtained access by exploiting Log4Shell in an unpatched VMware Horizon server. On or around January 30, likely shortly after the threat actors gained access, CISA observed the actors using PowerShell scripts [T1059.001] to callout to 109.248.150[.]13 via Hypertext Transfer Protocol (HTTP) [T1071.001] to retrieve additional PowerShell scripts. Around the same period, CISA observed the actors attempt to download [T1105] and execute a malicious file from 109.248.150[.]13. The activity started from IP address 104.155.149[.]103, which appears to be part of the actors’ C2 [TA0011] infrastructure.
After gaining initial access to the VMware Horizon server, the threat actors moved laterally [TA0008] via Remote Desktop Protocol (RDP) [T1021.001] to multiple other hosts in the production environment, including a security management server, a certificate server, a database containing sensitive law enforcement data, and a mail relay server. The threat actors also moved laterally via RDP to the organization’s disaster recovery network. The threat actors gained credentials [TA0006] for multiple accounts, including administrator accounts. It is unknown how these credentials were acquired.
After moving laterally to other production environment hosts and servers, the actors implanted loader malware on compromised servers containing executables enabling remote C2. The threat actors used compromised administrator accounts to run the loader malware. The loader malware appears to be modified versions of SysInternals LogonSessions, Du, or PsPing software. The embedded executables belong to the same malware family, are similar in design and functionality to 658_dump_64.exe, and provide C2 capabilities to a remote operator. These C2 capabilities include the ability to remotely monitor a system’s desktop, gain reverse shell access, exfiltrate data, and upload and execute additional payloads. The embedded executables can also function as a proxy.
CISA found the following loader malware:
For more information on these malware samples, including IOCs and detection signatures, see MAR-10382580-1.
Additionally, CISA identified a Java® Server Pages (JSP) application (error_401.js) functioning as a malicious webshell [T505.003] and a malicious Dynamic Link Library (DLL) file:
Threat actors collected [TA0009] and likely exfiltrated [TA0010] data from Victim 2’s production environment. For a three week period, the security management and certificate servers communicated with the foreign IP address 92.222.241[.]76. During this same period, the security management server sent more than 130 gigabytes (GB) of data to foreign IP address 92.222.241[.]76, indicating the actors likely exfiltrated data from the production environment. CISA also found .rar files containing sensitive law enforcement investigation data [T1560.001] under a known compromised administrator account.
Note: the second threat actor group had access to the organization’s test and production environments, and on or around April 13, 2022, leveraged CVE-2022-22954 to implant the Dingo J-spy webshell. According to trusted third-party reporting, multiple large organizations have been targeted by cyber actors leveraging CVE-2022-22954 and CVE-2022-22960. For more information on exploitation of CVE-2022-22954 and CVE-2022-22960, see CISA CSA Threat Actors Chaining Unpatched VMware Vulnerabilities for Full System Control.
If administrators discover system compromise, CISA and CGCYBER recommend:
CISA and CGCYBER recommend organizations install updated builds to ensure affected VMware Horizon and UAG systems are updated to the latest version.
Additionally, CISA and CGCYBER recommend organizations:
Recipients of this report are encouraged to contribute any additional information related to this threat.
[1] VMware Security Advisory VMSA-2021-0028.13
[2] Fortinet’s blog New Milestones for Deep Panda: Log4Shell and Digitally Signed Fire Chili Rootkits
See MAR-10382580-1 and MAR-10382254-1 and Table 1 for IOCs. See the list below to download copies of these IOCs:
Table 1: Indicators of Compromise
See Table 2 for the threat actors’ tactics and techniques identified in this CSA. See the MITRE ATT&CK for Enterprise framework, version 11, for all referenced threat actor tactics and techniques.
Table 2: Tactics and Techniques
Execution [TA0002]
© 2021 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation.
CISA and CGCYBER would like to thank VMware and Secureworks for their contributions to this CSA.
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