Hunters International is a ransomware strain operated under the Ransomware-as-a-Service (RaaS) business model that has been active since at least October 2023. Its primary objective is to exfiltrate sensitive data and subsequently extort victims by demanding ransom payments in exchange for the return or non-disclosure of the stolen information.

Malware analysis indicates that the Hunters International ransomware code contains approximately 60% code overlap with samples of Hive ransomware version 61. Hive ransomware, another prominent RaaS strain, was active from June 2021 until January 2023, when the Federal Bureau of Intelligence (FBI) collaborated with law enforcement agencies in Germany and the Netherlands to successfully dismantle its operation.

Technical analysis suggests a realistic possibility that Hunters International may have been deployed by actors linked to the disrupted Hive operation. However, while it bears significant similarities, Hunters International is not a direct rebrand. The operators have publicly denied affiliation with the Hive group, claiming they adopted Hive’s encryption logic while resolving several issues that previously caused file decryption failures.

AttackIQ has previously emulated Hive ransomware through the release of an attack graph in response to CISA Advisory AA22-321A.

AttackIQ has released a new attack graph that emulates the post-compromise Tactics, Techniques, and Procedures (TTPs) associated with the deployment of Hunters International to help customers validate their security controls and their ability to defend against this disruptive and destructive threat.

Validating your security program performance against these behaviors is vital in reducing risk. By using this new attack graph in the AttackIQ Security Optimization Platform, security teams will be able to:

  • Evaluate security control performance against baseline behaviors associated with the Hunters International ransomware.
  • Assess their security posture against an opportunistic adversary, which does not discriminate when it comes to selecting its targets.
  • Continuously validate detection and prevention pipelines against a playbook similar to those of many of the groups currently focused on ransomware activities.

[Malware Emulation] Hunters International Ransomware – 2024-07 – Associated Tactics, Techniques and Procedures (TTPs)

This attack graph seeks to emulate the sequence of behaviors associated with the deployment of Hunters International ransomware on a compromised system with the intent of providing customers with opportunities to prevent and/or detect a compromise in progress.

The assessment template is based on behaviors reported by Acronis on July 1, 2024, and Joe Sandbox on April 16, 2024.

Initial Access, Discovery & Impact – Ransomware Deployment and System Recovery Inhibition

This stage begins with the deployment of a Hunters International sample and proceeds to the deletion of Volume Shadow Copies using vssadmin.exe or wmic.exe. Once completed, it continues with obtaining a user’s token for subsequent impersonation. Following this, it will enumerate active processes and services using the Windows API.

Ingress Tool Transfer (T1105): This scenario downloads to memory and saves to disk in independent scenarios to test network and endpoint controls and their ability to prevent the delivery of known malicious samples.

Inhibit System Recovery (T1490): This scenario executes the vssadmin.exe utility to delete a recent Volume Shadow Copy created by the assessment template.

Inhibit System Recovery (T1490): This scenario executes the wmic.exe utility to delete a recent Volume Shadow Copy created by the assessment template.

Access Token Manipulation: Token Impersonation/Theft (T1134.001): This scenario lists active access tokens that are used to impersonate a user by another process.

Process Discovery (T1057): This scenario uses the Windows API to retrieve a list of running processes by calling CreateToolhelp32Snapshot and iterating through each process object with Process32FirstW and Process32NextW.

System Service Discovery (T1007): This scenario uses the EnumServicesStatus Windows API to gather information about configured services and retrieve details such as service name, service display name, and current service status.

Impact – Hunters International Ransomware Encryption

This stage begins by gathering information about the system, its drives and its file system using the Windows API. Once completed, it encrypts files using an encryption routine similar to Hunters International, which is a combination of AES-256 CBC + RSA-2048.

System Information Discovery (T1082): This scenario executes the GetSystemInfo Windows API to discover the processor architecture, page size, and number of logical processors.

Peripheral Device Discovery (T1120): This scenario retrieves information about the system’s physical disks using the GetLogicalDriveStringsW and GetDriveTypeW API calls.

File and Directory Discovery (T1083): This scenario will call the FindFirstFileW and FindNextFileW Windows API to perform the enumeration of the file system.

Data Encrypted for Impact (T1486): This scenario performs the file encryption routines used by common ransomware families. Files matching an extension list are identified and encrypted in place using similar encryption algorithms as used by Hunters International ransomware.

Detection and Mitigation Opportunities

Given the number of different techniques being utilized by this threat, it can be difficult to know which to prioritize for prevention and detection opportunities. AttackIQ recommends first focusing on the following techniques emulated in our scenarios before moving on to the remaining techniques.

1. Ingress Tool Transfer (T1105):

This actor relies heavily in downloading additional stages of malware. Endpoint and Network security controls should both be employed to try and detect the delivery of these malicious payloads.

1a. Detection

The following signatures can help identify when native utilities are being used to download malicious payloads.

PowerShell Example:

Process Name == (Cmd.exe OR Powershell.exe)
Command Line CONTAINS ((“IWR” OR “Invoke-WebRequest") AND “DownloadData” AND “Hidden”)

1b. Mitigation

MITRE ATT&CK has the following mitigation recommendations.

2. Inhibit System Recovery (T1490):

Adversaries often delete Volume Shadow Copies to prevent the possibility of restoring files back to their original state. This is a common technique used by ransomware as it prevents the recovery of files once the ransomware encryption routine successfully completes execution.

2a. Detection

Detecting deletion of Volume Shadow Copies is usually the first step that occurs and can be detected by looking at the command line activity

Process Name == (cmd.exe OR powershell.exe)
Command Line CONTAINS (“vssadmin” AND “Delete Shadows”)

2b. Mitigation

MITRE ATT&CK has the following mitigation recommendations for Inhibit System Recovery

3. Data Encrypted for Impact (T1486):

Preventing systems and files from being encrypted should be a top priority. Ensuring that you have layered endpoint defenses including Antivirus and EDR solutions is critical.

3a. Detection

Ransomware attacks are best prevented and alerted by your EDR/AV Policies. Typically, a configuration for ransomware protection is presented and we strongly encourage that it is enabled in your security controls.

There are three telling signs of ransomware activity in an environment that you could query for and possibly make preventative detections if your security controls allow. Those three are deletion of shadow volumes, suspicious amounts of exfiltrated data, and of course, wide set file encryption.

Detecting deletion of shadow volumes is usually the first step that occurs and can be detected by looking at command line activity:

Via vssadmin.exe:

Process Name == (cmd.exe OR powershell.exe)
Command Line CONTAINS (“vssadmin” AND “Delete Shadows”)

Via PowerShell:

Process Name == powershell.exe
Command Line == “Get-WmiObject Win32_Shadowcopy | ForEach-Object ($_.Delete();)”

Detecting suspicious Data Exfiltration:

Detecting exfiltration is well suited for IDS/IPS and DLP solutions. These products should be configured to identify sensitive files. If sensitive files, or a large amount of web traffic is sent to a rare external IP, it should be detected or prevented depending on security policies for the security control. Historical NetFlow data logging can also bubble up hosts that are experience uncommon peaks in outgoing traffic.

Detecting Ransomware-like File Encryption

Utilizing an EDR or SIEM/SOAR product can help detect and prevent suspicious file encryption related to ransomware attacks. Utilizing these tools to look for excessive file modifications (greater than 1000 on a system) within less than a minute of time is a good starting indicator.

To increase the fidelity, you could include file modification of file extensions to popular ransomware extensions such as .conti, .Locky, .Ryuk, etc. If possible, with a SOAR or preventative EDR platform, we recommend setting these detections to kill all processes involved in creating the alert as it will most likely stop the spread of the Ransomware.

3b. Mitigation

MITRE ATT&CK Recommends the following mitigations:

Wrap-up

In summary, this attack graph will evaluate security and incident response processes and support the improvement of your security control posture against the behaviors exhibited by Hunters International ransomware operators. With data generated from continuous testing and use of this assessment template, you can focus your teams on achieving key security outcomes, adjust your security controls, and work to elevate your total security program effectiveness against a known and dangerous threat.

AttackIQ offers a comprehensive Breach and Attack Simulation Platform to assist security teams. This includes AttackIQ Flex, a tailored pay-as-you-go service; AttackIQ Ready!, a fully managed service for continuous security optimization; and AttackIQ Enterprise, a co-managed service offering enhanced support. These services ensure your team maintains a robust security posture.