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Ransomware group targeting VPN servers

CISA have released a warning of the threat posed by ransomware operators ‘Daixin’, who are heavily targeting healthcare providers, using double extortion tactics to facilitate payment.

Daixin’s most common method of gaining initial access to their victim’s networks is by compromising Virtual Private Network (VPN) servers, achieved through exploitation of existing vulnerabilities, typically found in a legacy server or from successful use of a user’s login credentials.

From this stage the group will seek to move through the network via secure shell (SSH) and remote desktop protocol (RDP) and escalate privileges using pass the hash techniques.

Following this, the threat actor can authenticate by using a valid users’ credentials, despite not having access to them in cleartext.

The group’s typical modus operandi is to target VMware ESXi servers. From here they will seek to exfiltrate sensitive information using Ngrok - a reverse proxy which can establish connections without the need for network address translation (NAT) on firewalls or routers.

In turn, this allows the group to establish a connection between the compromised ESXi server and the internet by using a URL generated by Ngrok.

After the exfiltration of sensitive information used to further extort the victim, Daixin will deploy ransomware which is reportedly based upon the leaked source code of the Babuk Locker group (who notably refrain from targeting healthcare providers).

A ransom note is left for the victim with a payment demand which is usually requested within five days.

It is recommended to remove legacy and end-of-life systems, particularly those that are internet facing as they provide a significant risk to the security posture of the organisation.

Beyond sound patch maintenance, use of MFA and network segmentation, it is also advisable to implement blocks for proxies that can be used to exfiltrate information as mentioned above with the use of Ngrok.

To protect against pass the hash techniques, implement a password policy that mitigates the use of overlapping passwords, this will protect against lateral movement across multiple systems.



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