Threats Behind the Mask of Gentlemen Ransomware
Summary:
Gentlemen is a new ransomware group that emerged around August 2025. Like any other ransomware operation, the gang operates a double extortion model, where it will exfiltrate data and encrypt systems to pressure victims into complying with ransom demands. Gentlemen’s encryptor is developed in the Go programming language and is controlled through execution parameters, including a mandatory password check that prevents accidental execution on unintended environments. The encryptor uses the X25519 and XChaCha20 encryption algorithms to lock files of interest. Notably, when dealing with large files, the ransomware only selects segments of the files, ensuring fast encryption speeds.
Gentlemen employs several techniques to ensure successful encryption and evade security defenses. The ransomware disables Windows Defender to prevent any interruptions during the encryption process. It also deletes logs, making it difficult for security professionals to trace back the activity. Backup services like Veeam, and database-related services such as MSSQL and MongoDB are further terminated, preventing victims from recovering their data.
Security Officer Comments:
Since initiating operations in August of this year, Gentlemen has grown to be a prominent threat within the ransomware landscape. The group has targeted dozens of organizations in at least 17 countries, impacting a range of industries such as manufacturing, construction, healthcare, and insurance. Based on attacks observed to date, Gentlemen primarily targets medium to large organizations, ensuring higher ransom payouts and greater operational impact. As of writing, there is no evidence that Gentlemen operates as a Ransomware as a Service (RaaS) model or whether the group is a rebranding of an existing ransomware group. This suggests that Gentlemen is a well-funded independent group with an advanced skillset.
Suggested Corrections:
Backup your data, system images, and configurations, regularly test them, and keep the backups offline: Ensure that backups are regularly tested and that they are not connected to the business network, as many ransomware variants try to find and encrypt or delete accessible backups. Maintaining current backups offline is critical because if your network data is encrypted with ransomware, your organization can restore systems.
Update and patch systems promptly: This includes maintaining the security of operating systems, applications, and firmware in a timely manner. Consider using a centralized patch management system; use a risk-based assessment strategy to drive your patch management program.
Test your incident response plan: There's nothing that shows the gaps in plans more than testing them. Run through some core questions and use those to build an incident response plan: Are you able to sustain business operations without access to certain systems? For how long? Would you turn off your manufacturing operations if business systems such as billing were offline?
Check your security team's work: Use a 3rd party pen tester to test the security of your systems and your ability to defend against a sophisticated attack. Many ransomware criminals are aggressive and sophisticated and will find the equivalent of unlocked doors.
Segment your networks: There's been a recent shift in ransomware attacks – from stealing data to disrupting operations. It's critically important that your corporate business functions and manufacturing/production operations are separated and that you carefully filter and limit internet access to operational networks, identify links between these networks, and develop workarounds or manual controls to ensure ICS networks can be isolated and continue operating if your corporate network is compromised. Regularly test contingency plans such as manual controls so that safety-critical functions can be maintained during a cyber incident.
Train employees: Email remains the most vulnerable attack vector for organizations. Users should be trained on how to avoid and spot phishing emails.
Implement multi-factor authentication (MFA): External-facing assets that leverage single-factor authentication (SFA) are highly susceptible to brute-forcing attacks, password spraying, or unauthorized remote access using valid (stolen) credentials. Implementing MFA enhances security and adds an extra layer of protection.
Link(s):
https://asec.ahnlab.com/en/91545/
Gentlemen is a new ransomware group that emerged around August 2025. Like any other ransomware operation, the gang operates a double extortion model, where it will exfiltrate data and encrypt systems to pressure victims into complying with ransom demands. Gentlemen’s encryptor is developed in the Go programming language and is controlled through execution parameters, including a mandatory password check that prevents accidental execution on unintended environments. The encryptor uses the X25519 and XChaCha20 encryption algorithms to lock files of interest. Notably, when dealing with large files, the ransomware only selects segments of the files, ensuring fast encryption speeds.
Gentlemen employs several techniques to ensure successful encryption and evade security defenses. The ransomware disables Windows Defender to prevent any interruptions during the encryption process. It also deletes logs, making it difficult for security professionals to trace back the activity. Backup services like Veeam, and database-related services such as MSSQL and MongoDB are further terminated, preventing victims from recovering their data.
Security Officer Comments:
Since initiating operations in August of this year, Gentlemen has grown to be a prominent threat within the ransomware landscape. The group has targeted dozens of organizations in at least 17 countries, impacting a range of industries such as manufacturing, construction, healthcare, and insurance. Based on attacks observed to date, Gentlemen primarily targets medium to large organizations, ensuring higher ransom payouts and greater operational impact. As of writing, there is no evidence that Gentlemen operates as a Ransomware as a Service (RaaS) model or whether the group is a rebranding of an existing ransomware group. This suggests that Gentlemen is a well-funded independent group with an advanced skillset.
Suggested Corrections:
Backup your data, system images, and configurations, regularly test them, and keep the backups offline: Ensure that backups are regularly tested and that they are not connected to the business network, as many ransomware variants try to find and encrypt or delete accessible backups. Maintaining current backups offline is critical because if your network data is encrypted with ransomware, your organization can restore systems.
Update and patch systems promptly: This includes maintaining the security of operating systems, applications, and firmware in a timely manner. Consider using a centralized patch management system; use a risk-based assessment strategy to drive your patch management program.
Test your incident response plan: There's nothing that shows the gaps in plans more than testing them. Run through some core questions and use those to build an incident response plan: Are you able to sustain business operations without access to certain systems? For how long? Would you turn off your manufacturing operations if business systems such as billing were offline?
Check your security team's work: Use a 3rd party pen tester to test the security of your systems and your ability to defend against a sophisticated attack. Many ransomware criminals are aggressive and sophisticated and will find the equivalent of unlocked doors.
Segment your networks: There's been a recent shift in ransomware attacks – from stealing data to disrupting operations. It's critically important that your corporate business functions and manufacturing/production operations are separated and that you carefully filter and limit internet access to operational networks, identify links between these networks, and develop workarounds or manual controls to ensure ICS networks can be isolated and continue operating if your corporate network is compromised. Regularly test contingency plans such as manual controls so that safety-critical functions can be maintained during a cyber incident.
Train employees: Email remains the most vulnerable attack vector for organizations. Users should be trained on how to avoid and spot phishing emails.
Implement multi-factor authentication (MFA): External-facing assets that leverage single-factor authentication (SFA) are highly susceptible to brute-forcing attacks, password spraying, or unauthorized remote access using valid (stolen) credentials. Implementing MFA enhances security and adds an extra layer of protection.
Link(s):
https://asec.ahnlab.com/en/91545/