Executive Summary

Since May 2023, Arete’s Incident Response (IR) team has responded to multiple BlackSuit ransomware engagements against organizations in the healthcare, financial services, manufacturing, professional services, public service, entertainment, and retail sectors. This spotlight explores the ransomware behavior observed, statistics from IR engagements, and background information on the threat actor. Finally, we discuss security recommendations to better defend against this evolving cyber threat and mitigate the risk of financial and reputational losses arising from these incidents.

Incident Response Data on BlackSuit Ransomware

The information below is based on BlackSuit incidents investigated by Arete since May 2023. Our IR and teams work together to analyze key data points during every ransomware engagement and form real-time threat actor (TA) insights.

• Arete has investigated dozens of engagements involving BlackSuit.

• We have been extremely successful in negotiating discounted ransoms with this TA.

• The highest observed ransom demand is around $18 million.

• The average initial demand is around $2.5 million.

• The average ransom payment facilitated is around $500,000.

• Commonly observed methods of intrusions include remote desktop protocol (RDP), virtual private network (VPN), and firewall vulnerabilities.

• Tools observed during the investigations include CobaltStrike, WinRAR, PUTTY, Rclone, Advanced IP Scanner, Network Scanner, Mimikatz, and GMER.

• A commonly observed ransom note filename is readme.blacksuit.txt.

• In some instances, backups were encrypted or deleted, while in others, backups were used for restoration.

Background

The information about the BlackSuit threat actor group in this section was shared in Arete’s 2024 Q1 Crimeware Report.

The most notable newcomer in Q1 was BlackSuit, the third most active group of Q1. Although Arete first observed BlackSuit ransomware operating in May 2023, it only accounted for less than a half percent of the total engagements in 2023. The group significantly increased its activity in Q1 2024, and there were more BlackSuit engagements in February 2024 alone than in all of 2023. BlackSuit operates as a private group without affiliates, targeting both Windows and Linux users and utilizing a double extortion method of stealing and encrypting sensitive data on a victim’s network.

BlackSuit: A Continuation of Royal Ransomware?

The BlackSuit ransomware payload has significant code overlap with Royal ransomware, and the Cybersecurity and Infrastructure Security Agency (CISA) and the FBI believe BlackSuit to likely be a rebranding or spinoff variant of Royal. While BlackSuit could be using the same developer or code with slight modifications, Arete also observed language used by BlackSuit in ransom negotiations identical to previous engagements with Royal, which lends to the assessment that the group might be a rebrand or offshoot. Regardless, BlackSuit’s emergence demonstrates that although names may change, threat actors will find ways to adapt and evolve their operations.

Figure 1. Language from two separate BlackSuit TOR chats (Source: Arete)

Figure 2. Identical language from two separate Royal TOR chats (Source: Arete)

Technical Analysis

Malware analysis revealed that BlackSuit ransomware:

• Supports multiple command-line arguments.

• Encrypts files on the system and mounted shares.

• Adds the following extension to encrypted files: .blacksuit (e.g., file.docx.blacksuit).

• Creates a ransom note with the following filename: readme.blacksuit.txt.

• Self-identifies the group as BlackSuit in the ransom note.

• References a data leak site in the ransom note that, when accessed, self-identifies the group as BlackSuit.

• Kills a list of processes and services.

• Maintains a list of whitelisted files and directories to make sure it will not render the system unusable, preventing recovery when running a decryptor.

• Attempts to prevent system recovery by deleting the system’s volume shadow copies.

• Creates the following mutex during execution: WLm87eV1oNRx6P3E4Cy9.

Execution Pattern/Arguments

BlackSuit ransomware needs command line arguments to execute and encrypt files in the system. Command line arguments supported:

The ransomware will not execute in the system without the “–id” argument followed by a 32-character value that is unique in each engagement and present in the ransom note TOR URL. Portion of the data in the ransom note that contains the ID:

Execution of ransomware to encrypt files:

The ransomware developer coded the logic to allow configuration of the 32-character value in the command line during execution. This same victim-specific 32-character string value is then added to the ransom note URL used for negotiations. Due to this implementation in the ransomware code, threat researchers can execute the ransomware without knowing the 32-character string value, as any value of this type can be used to execute the malicious code. In analyzing Royal ransomware samples, Arete found a similarity in that any 32-character value can be supplied to execute the ransomware, and the value is also added to the ransom note TOR chat URL.

Example of how the ransom note content looks with a randomly supplied string (e.g., blacksuit.exe -id 7777777777777777777777777777777):

Obfuscated Files or Information: Software Packing

Most of the strings in the ransomware are encoded. The encoded strings are hardcoded and decoded at runtime. Every encoded string has its own decoding loop:

Figure 3. Encoded strings hardcoded

Figure 4. String decoding loop

Some relevant strings decoded in memory:

Obfuscated Files or Information: Dynamic API Resolution

To avoid static or other defensive analysis, the ransomware uses dynamic API resolution to conceal malware characteristics and functionality. The ransomware initially decrypts DLL names, then loads the APIs. Hardcoded encoded DLL names are shown below:

Figure 5. Encoded DLL names

Figure 6. DLL name decoding loop

DLL names decoded at runtime:

Stop Services and Processes

Before file encryption, the ransomware terminates a list of known running processes and services to encrypt as many files as possible. BlackSuit ransomware utilizes the Windows Restart Manager to terminate any process using files other than explorer.exe or a critical process.

Sequence of Windows Restart Manager APIs used by the ransomware:

The ransomware also uses Windows native CreateToolhelp32Snapshot, Process32FirstW, and Process32NextW APIs to enumerate processes in the system.

File and Directory Exclusions

The ransomware excludes system-related files and folders, ransomware-related files, and whitelisted extensions during encryption.

Excluded file extensions:

Excluded files and directories:

Inhibit System Recovery

Windows operating systems contain features that can help fix corrupted system files, including shadow copies, which are backups of files created by the Volume Shadow Copy Service (VSS). By deleting shadow copies, the ransomware can prevent victims from restoring files from backups, making it more difficult for them to recover their data without paying the ransom.

With the CreateProcessW function, the ransomware deletes volume shadow copies before file encryption by executing the following command:

Code in the ransomware showing this operation (the EAX register contains the kernel32.CreateProcessW address):

Figure 7. Create process call to delete volume shadow copies

System Network Connections Discovery

BlackSuit ransomware can enumerate network-mounted shares by scanning the network interfaces.

Data Encrypted for Impact

The ransomware initially finds available drives and loads the files one by one using the Windows API FindFirstFileW and FindNextFileW. It then uses OpenSSL AES keys to encrypt the files and adds the extension .blacksuit to the encrypted file name.

Figure 8. Windows native CryptEncrypt API call to encrypt the data

Public key:

The ransomware encrypts files, adds the .blacksuit extension at the end of the encrypted files, and adds the following bytes at the end of the file (“??” represents variable bytes):

Figure 9. “.blacksuit” extension added to the encrypted files

Figure 10. Padding bytes in encrypted files

Upon successful execution, the ransomware creates ransom notes with the file name readme.blacksuit.txt.

Figure 11. Screenshot of BlackSuit ransom note

Modify Registry

The ransomware did not perform any registry key modification.

Mutex

The mutex is the fundamental tool for managing shared resources between multiple threads or processes. Typically, ransomware uses a mutex to avoid reinfecting the victim system and causing multiple layers of encryption. The ransomware creates the following mutex value: “WLm87eV1oNRx6P3E4Cy9”.

Figure 12. Screenshot of the mutex value created while debugging the ransomware

Network Activity

The ransomware did not try to communicate with a remote server other than encrypting data from mounted shares.

Indicators of Compromise

Data Leak Site

The ransom note contains a data leak site (DLS) that displayed the following page, self-identifying the group as BlackSuit:

Figure 13. TOR DLS: c7jpc6h2ccrdwmhofuij7kz6sr2fg2ndtbvvqy4fse23cf7m2e5hvqid[.]onion

Figure 14. TOR DLS: weg7sdx54bevnvulapqu6bpzwztryeflq3s23tegbmnhkbpqz637f2yd[.]onion

Detection Mechanisms

Custom Detections and Blocking with Arete’s Arsinal

Yara

Recommended Mitigations

• Utilize an endpoint detection and response (EDR) solution with the capability to halt detected processes and isolate systems on the network based on identified conditions.

• Block any known attacker C2s in the firewall.

• Implement multi-factor authentication on RDP and VPN to restrict access to critical network resources.

• Eliminate unnecessary RDP ports exposed to the internet.

• Block a high number of SMB connection attempts from one system to others in the network over a short period of time.

• Perform periodic dark web monitoring to verify if data is available for sale on the black market.

• Perform penetration tests.

• Periodically patch systems and update tools.

• Monitor connections to the network from suspicious locations.

• Monitor downloads and uploads of files to file-sharing services outside standard work hours.

• Monitor file uploads from domain controllers to the internet.

• Monitor network scans from uncommon servers (e.g., RDP server).

Organizations can find the full list of US government recommended ransomware prevention and mitigation guidance here: https://www.cisa.gov/stopransomware/ransomware-guide.

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References

• Arete Releases Q1 2024 Crimeware Report Detailing Ransomware and Extortion Trends and Shifts in the Cyber Threat Landscape 

• Arsinal Threat Management

• Multiple car dealers report disruptions to SEC due to cyberattack on software company

• CDK Hackers Want Millions in Ransom to End Car Dealership Outage

• BlackSuit Cybercrime Gang Blamed in CDK Hack That Roiled Car Dealers