New BYOVD Loader Behind Deadlock Ransomware Attack
Summary:
Cisco Talos tracked new TTPs from a financially motivated threat actor that were utilized to deploy DeadLock ransomware on Windows machines. The key initial access technique involves a BYOVD attack using the legitimate but vulnerable Baidu Antivirus driver (disguised as DriverGay.sys) to exploit CVE-2024-51324. This vulnerability is an Improper Privilege Management flaw that allows the actor, via a custom loader (EDRGay.exe), to execute a kernel-level command to terminate any process, specifically targeting and disabling EDR solutions. The loader establishes communication with the driver using the CreateFile() API and triggers the exploit using the DeviceIOControl() function with a specific I/O Control Code to execute the ZwTerminateProcess() command.
Pre-encryption activities involve a PowerShell script to prepare the system that bypasses User Account Control, disables Windows Defender, terminates various security, backup, and database services, and deletes all volume shadow copies. The actor maintains basic system functionality by excluding core services from being terminated. Cisco Talos suspects the actor gained initial access through compromised valid accounts. They establish persistence and remote access by modifying registry settings to enable RDP connections (opening port 3389), starting the RemoteRegistry service, and installing AnyDesk. The final payload, DeadLock ransomware, uses a custom stream cipher encryption algorithm with time-based cryptographic keys to selectively and effectively encrypt files. This method, along with anti-forensics techniques, complicates data recovery. The threat actor, active since July 2025, compels victims to communicate via the Session messenger rather than operating a traditional data leak site.
Security Officer Comments:
This attack chain highlights a concerning evolution in ransomware defense evasion tactics, specifically the calculated use of the BYOVD technique as the primary EDR evasion mechanism. The exploitation of a signed, legitimate driver's kernel-level function to bypass security controls demonstrates a focus on the manipulation of system resources. The pre-encryption PowerShell phase is lengthy, focusing on diminishing the victim’s recovery capability by comprehensively disabling recovery and security safeguards with anti-forensics techniques while carefully ensuring the services necessary for coercing victims toward ransom payment remain intact. The reliance on compromised credentials for initial access and the subsequent setup of multiple remote access methods (RDP/AnyDesk) further emphasizes the redundancy of their persistence baked into this operation.
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://blog.talosintelligence.com/byovd-loader-deadlock-ransomware/
Cisco Talos tracked new TTPs from a financially motivated threat actor that were utilized to deploy DeadLock ransomware on Windows machines. The key initial access technique involves a BYOVD attack using the legitimate but vulnerable Baidu Antivirus driver (disguised as DriverGay.sys) to exploit CVE-2024-51324. This vulnerability is an Improper Privilege Management flaw that allows the actor, via a custom loader (EDRGay.exe), to execute a kernel-level command to terminate any process, specifically targeting and disabling EDR solutions. The loader establishes communication with the driver using the CreateFile() API and triggers the exploit using the DeviceIOControl() function with a specific I/O Control Code to execute the ZwTerminateProcess() command.
Pre-encryption activities involve a PowerShell script to prepare the system that bypasses User Account Control, disables Windows Defender, terminates various security, backup, and database services, and deletes all volume shadow copies. The actor maintains basic system functionality by excluding core services from being terminated. Cisco Talos suspects the actor gained initial access through compromised valid accounts. They establish persistence and remote access by modifying registry settings to enable RDP connections (opening port 3389), starting the RemoteRegistry service, and installing AnyDesk. The final payload, DeadLock ransomware, uses a custom stream cipher encryption algorithm with time-based cryptographic keys to selectively and effectively encrypt files. This method, along with anti-forensics techniques, complicates data recovery. The threat actor, active since July 2025, compels victims to communicate via the Session messenger rather than operating a traditional data leak site.
Security Officer Comments:
This attack chain highlights a concerning evolution in ransomware defense evasion tactics, specifically the calculated use of the BYOVD technique as the primary EDR evasion mechanism. The exploitation of a signed, legitimate driver's kernel-level function to bypass security controls demonstrates a focus on the manipulation of system resources. The pre-encryption PowerShell phase is lengthy, focusing on diminishing the victim’s recovery capability by comprehensively disabling recovery and security safeguards with anti-forensics techniques while carefully ensuring the services necessary for coercing victims toward ransom payment remain intact. The reliance on compromised credentials for initial access and the subsequent setup of multiple remote access methods (RDP/AnyDesk) further emphasizes the redundancy of their persistence baked into this operation.
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://blog.talosintelligence.com/byovd-loader-deadlock-ransomware/