• Enforce multifactor authentication (MFA) on all user accounts.
• Implement network segmentation to separate network segments based on role and functionality.
• Update software, including operating systems, applications, and firmware, on network assets.
• Audit account usage.
From November 2021 through January 2022, the Cybersecurity and Infrastructure Security Agency (CISA) responded to advanced persistent threat (APT) activity on a Defense Industrial Base (DIB) Sector organization’s enterprise network. During incident response activities, CISA uncovered that likely multiple APT groups compromised the organization’s network, and some APT actors had long-term access to the environment. APT actors used an open-source toolkit called Impacket to gain their foothold within the environment and further compromise the network, and also used a custom data exfiltration tool, CovalentStealer, to steal the victim’s sensitive data.
This joint Cybersecurity Advisory (CSA) provides APT actors tactics, techniques, and procedures (TTPs) and indicators of compromise (IOCs) identified during the incident response activities by CISA and a third-party incident response organization. The CSA includes detection and mitigation actions to help organizations detect and prevent related APT activity. CISA, the Federal Bureau of Investigation (FBI), and the National Security Agency (NSA) recommend DIB sector and other critical infrastructure organizations implement the mitigations in this CSA to ensure they are managing and reducing the impact of cyber threats to their networks.
For a downloadable copy of IOCs, see the following files:
- Malware Analysis Report (MAR)-10365227-1.stix, 966 kb
- MAR-10365227-2.stix, 249B
- MAR-10365227-3.stix, 3.2 MB
Technical Details
Threat Actor Activity
Note: This advisory uses the MITRE ATT&CK® for Enterprise framework, version 11. See the MITRE ATT&CK Tactics and Techniques section for a table of the APT cyber activity mapped to MITRE ATT&CK for Enterprise framework.
From November 2021 through January 2022, CISA conducted an incident response engagement on a DIB Sector organization’s enterprise network. The victim organization also engaged a third-party incident response organization for assistance. During incident response activities, CISA and the trusted –third-party identified APT activity on the victim’s network.
Some APT actors gained initial access to the organization’s Microsoft Exchange Server as early as mid-January 2021. The initial access vector is unknown. Based on log analysis, the actors gathered information about the exchange environment and performed mailbox searches within a four-hour period after gaining access. In the same period, these actors used a compromised administrator account (“Admin 1”) to access the EWS Application Programming Interface (API). In early February 2021, the actors returned to the network and used Admin 1 to access EWS API again. In both instances, the actors used a virtual private network (VPN).
Four days later, the APT actors used Windows Command Shell over a three-day period to interact with the victim’s network. The actors used Command Shell to learn about the organization’s environment and to collect sensitive data, including sensitive contract-related information from shared drives, for eventual exfiltration. The actors manually collected files using the command-line tool, WinRAR. These files were split into approximately 3MB chunks located on the Microsoft Exchange server within the directory. See Appendix: Windows Command Shell Activity for additional information, including specific commands used.
During the same period, APT actors implanted Impacket, a Python toolkit for programmatically constructing and manipulating network protocols, on another system. The actors used Impacket to attempt to move laterally to another system.
In early March 2021, APT actors exploited CVE-2021-26855, CVE-2021-26857, CVE-2021-26868, and CVE-2021-27065 to install 17 China Chopper webshells on the Exchange Server. Later in March, APT actors installed HyperBro on the Exchange Server and two other systems. For more information on the HyperBro and webshell samples, see CISA MAR-10365227-2 and -3.
In April 2021, APT actors used Impacket for network exploitation activities. See the Use of Impacket section for additional information. From late July through mid-October 2021, APT actors employed a custom exfiltration tool, CovalentStealer, to exfiltrate the remaining sensitive files. See the Use of Custom Exfiltration Tool: CovalentStealer section for additional information.
APT actors maintained access through mid-January 2022, likely by relying on legitimate credentials.
Use of Impacket
CISA discovered activity indicating the use of two Impacket tools: and . These tools use Windows Management Instrumentation (WMI) and Server Message Block (SMB) protocol, respectively, for creating a semi-interactive shell with the target device. Through the Command Shell, an Impacket user with credentials can run commands on the remote device using the Windows management protocols required to support an enterprise network.
The APT cyber actors used existing, compromised credentials with Impacket to access a higher privileged service account used by the organization’s multifunctional devices. The threat actors first used the service account to remotely access the organization’s Microsoft Exchange server via Outlook Web Access (OWA) from multiple external IP addresses; shortly afterwards, the actors assigned the Application Impersonation role to the service account by running the following PowerShell command for managing Exchange:
This command gave the service account the ability to access other users’ mailboxes.
The APT cyber actors used virtual private network (VPN) and virtual private server (VPS) providers, M247 and SurfShark, as part of their techniques to remotely access the Microsoft Exchange server. Use of these hosting providers, which serves to conceal interaction with victim networks, are common for these threat actors. According to CISA’s analysis of the victim’s Microsoft Exchange server Internet Information Services (IIS) logs, the actors used the account of a former employee to access the EWS. EWS enables access to mailbox items such as email messages, meetings, and contacts. The source IP address for these connections is mostly from the VPS hosting provider, M247.
Use of Custom Exfiltration Tool: CovalentStealer
The threat actors employed a custom exfiltration tool, CovalentStealer, to exfiltrate sensitive files.
CovalentStealer is designed to identify file shares on a system, categorize the files, and upload the files to a remote server. CovalentStealer includes two configurations that specifically target the victim’s documents using predetermined files paths and user credentials. CovalentStealer stores the collected files on a Microsoft OneDrive cloud folder, includes a configuration file to specify the types of files to collect at specified times and uses a 256-bit AES key for encryption. See CISA MAR-10365227-1 for additional technical details, including IOCs and detection signatures.
MITRE ATT&CK Tactics and Techniques
MITRE ATT&CK is a globally accessible knowledge base of adversary tactics and techniques based on real-world observations. CISA uses the ATT&CK Framework as a foundation for the development of specific threat models and methodologies. Table 1 lists the ATT&CK techniques employed by the APT actors.
|
Initial Access |
||
|
Technique Title |
ID |
Use |
| Valid Accounts | T1078 | Actors obtained and abused credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. In this case, they exploited an organization’s multifunctional device domain account used to access the organization’s Microsoft Exchange server via OWA. |
|
Execution |
||
|
Technique Title |
ID |
Use |
| Windows Management Instrumentation | T1047 | Actors used Impacket tools wmiexec.py and smbexec.py to leverage Windows Management Instrumentation and execute malicious commands. |
| Command and Scripting Interpreter | T1059 | Actors abused command and script interpreters to execute commands. |
| Command and Scripting Interpreter: PowerShell | T1059.001 | Actors abused PowerShell commands and scripts to map shared drives by specifying a path to one location and retrieving the items from another. See Appendix: Windows Command Shell Activity for additional information. |
| Command and Scripting Interpreter: Windows Command Shell | T1059.003 | Actors abused the Windows Command Shell to learn about the organization’s environment and to collect sensitive data. See Appendix: Windows Command Shell Activity for additional information, including specific commands used.
The actors used Impacket tools, which enable a user with credentials to run commands on the remote device through the Command Shell. |
| Command and Scripting Interpreter: Python | T1059.006 | The actors used two Impacket tools: wmiexec.py and smbexec.py. |
| Shared Modules | T1129 | Actors executed malicious payloads via loading shared modules. The Windows module loader can be instructed to load DLLs from arbitrary local paths and arbitrary Universal Naming Convention (UNC) network paths. |
| System Services | T1569 | Actors abused system services to execute commands or programs on the victim’s network. |
|
Persistence |
||
|
Technique Title |
ID |
Use |
| Valid Accounts | T1078 | Actors obtained and abused credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. |
| Create or Modify System Process | T1543 | Actors were observed creating or modifying system processes. |
|
Privilege Escalation |
||
|
Technique Title |
ID |
Use |
| Valid Accounts | T1078 | Actors obtained and abused credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. In this case, they exploited an organization’s multifunctional device domain account used to access the organization’s Microsoft Exchange server via OWA. |
|
Defense Evasion |
||
|
Technique Title |
ID |
Use |
| Masquerading: Match Legitimate Name or Location | T1036.005 | Actors masqueraded the archive utility WinRAR.exe by renaming it VMware.exe to evade defenses and observation. |
| Indicator Removal on Host | T1070 | Actors deleted or modified artifacts generated on a host system to remove evidence of their presence or hinder defenses. |
| Indicator Removal on Host: File Deletion | T1070.004 | Actors used the del.exe command with the /f parameter to force the deletion of read-only files with the *.rar and tempg* wildcards. |
| Valid Accounts | T1078 | Actors obtained and abused credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. In this case, they exploited an organization’s multifunctional device domain account used to access the organization’s Microsoft Exchange server via OWA. |
| Virtualization/Sandbox Evasion: System Checks | T1497.001 | Actors used Windows command shell commands to detect and avoid virtualization and analysis environments. See Appendix: Windows Command Shell Activity for additional information. |
| Impair Defenses: Disable or Modify Tools | T1562.001 | Actors used the taskkill command to probably disable security features. CISA was unable to determine which application was associated with the Process ID. |
| Hijack Execution Flow | T1574 | Actors were observed using hijack execution flow. |
|
Discovery |
||
|
Technique Title |
ID |
Use |
| System Network Configuration Discovery | T1016 | Actors used the systeminfo command to look for details about the network configurations and settings and determine if the system was a VMware virtual machine.
The threat actor used route print to display the entries in the local IP routing table. |
| System Network Configuration Discovery: Internet Connection Discovery | T1016.001 | Actors checked for internet connectivity on compromised systems. This may be performed during automated discovery and can be accomplished in numerous ways. |
| System Owner/User Discovery | T1033 | Actors attempted to identify the primary user, currently logged in user, set of users that commonly use a system, or whether a user is actively using the system. |
| System Network Connections Discovery | T1049 | Actors used the netstat command to display TCP connections, prevent hostname determination of foreign IP addresses, and specify the protocol for TCP. |
| Process Discovery | T1057 | Actors used the tasklist command to get information about running processes on a system and determine if the system was a VMware virtual machine.
The actors used tasklist.exe and find.exe to display a list of applications and services with their PIDs for all tasks running on the computer matching the string “powers.” |
| System Information Discovery | T1082 | Actors used the ipconfig command to get detailed information about the operating system and hardware and determine if the system was a VMware virtual machine. |
| File and Directory Discovery | T1083 | Actors enumerated files and directories or may search in specific locations of a host or network share for certain information within a file system. |
| Virtualization/Sandbox Evasion: System Checks | T1497.001 | Actors used Windows command shell commands to detect and avoid virtualization and analysis environments. |
|
Lateral Movement |
||
|
Technique Title |
ID |
Use |
| Remote Services: SMB/Windows Admin Shares | T1021.002 | Actors used Valid Accounts to interact with a remote network share using Server Message Block (SMB) and then perform actions as the logged-on user. |
|
Collection |
||
|
Technique Title |
ID |
Use |
| Archive Collected Data: Archive via Utility | T1560.001 | Actor used PowerShell commands and WinRAR to compress and/or encrypt collected data prior to exfiltration. |
| Data from Network Shared Drive | T1039 | Actors likely used net share command to display information about shared resources on the local computer and decide which directories to exploit, the powershell dir command to map shared drives to a specified path and retrieve items from another, and the ntfsinfo command to search network shares on computers they have compromised to find files of interest.
The actors used dir.exe to display a list of a directory’s files and subdirectories matching a certain text string. |
| Data Staged: Remote Data Staging | T1074.002 | The actors split collected files into approximately 3 MB chunks located on the Exchange server within the CU2\he\debug directory. |
|
Command and Control |
||
|
Technique Title |
ID |
Use |
| Non-Application Layer Protocol | T1095 | Actors used a non-application layer protocol for communication between host and Command and Control (C2) server or among infected hosts within a network. |
| Ingress Tool Transfer | T1105 | Actors used the certutil command with three switches to test if they could download files from the internet.
The actors employed CovalentStealer to exfiltrate the files. |
| Proxy | T1090 | Actors are known to use VPN and VPS providers, namely M247 and SurfShark, as part of their techniques to access a network remotely. |
|
Exfiltration |
||
|
Technique Title |
ID |
Use |
| Schedule Transfer | T1029 | Actors scheduled data exfiltration to be performed only at certain times of day or at certain intervals and blend traffic patterns with normal activity. |
| Exfiltration Over Web Service: Exfiltration to Cloud Storage | T1567.002 | The actor’s CovalentStealer tool stores collected files on a Microsoft OneDrive cloud folder. |
DETECTION
Given the actors’ demonstrated capability to maintain persistent, long-term access in compromised enterprise environments, CISA, FBI, and NSA encourage organizations to:
- Monitor logs for connections from unusual VPSs and VPNs. Examine connection logs for access from unexpected ranges, particularly from machines hosted by SurfShark and M247.
- Monitor for suspicious account use (e.g., inappropriate or unauthorized use of administrator accounts, service accounts, or third-party accounts). To detect use of compromised credentials in combination with a VPS, follow the steps below:
- Review logs for “impossible logins,” such as logins with changing username, user agent strings, and IP address combinations or logins where IP addresses do not align to the expected user’s geographic location.
- Search for “impossible travel,” which occurs when a user logs in from multiple IP addresses that are a significant geographic distance apart (i.e., a person could not realistically travel between the geographic locations of the two IP addresses in the time between logins). Note: This detection opportunity can result in false positives if legitimate users apply VPN solutions before connecting to networks.
- Search for one IP used across multiple accounts, excluding expected logins.
- Take note of any M247-associated IP addresses used along with VPN providers (e.g., SurfShark). Look for successful remote logins (e.g., VPN, OWA) for IPs coming from M247- or using SurfShark-registered IP addresses.
- Identify suspicious privileged account use after resetting passwords or applying user account mitigations.
- Search for unusual activity in typically dormant accounts.
- Search for unusual user agent strings, such as strings not typically associated with normal user activity, which may indicate bot activity.
- Review the YARA rules provided in MAR-10365227-1 to assist in determining whether malicious activity has been observed.
- Monitor for the installation of unauthorized software, including Remote Server Administration Tools (e.g., psexec, RdClient, VNC, and ScreenConnect).
- Monitor for anomalous and known malicious command-line use. See Appendix: Windows Command Shell Activity for commands used by the actors to interact with the victim’s environment.
- Monitor for unauthorized changes to user accounts (e.g., creation, permission changes, and enabling a previously disabled account).
CONTAINMENT AND REMEDIATION
Organizations affected by active or recently active threat actors in their environment can take the following initial steps to aid in eviction efforts and prevent re-entry:
- Report the incident. Report the incident to U.S. Government authorities and follow your organization’s incident response plan.
- Report incidents to CISA via CISA’s 24/7 Operations Center (report@cisa.gov or 888-282-0870).
- Report incidents to your local FBI field office at fbi.gov/contact-us/field-
offices or to FBI’s 24/7 Cyber Watch (CyWatch) via (855) 292-3937 or
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