The ESXi host Secure Shell (SSH) daemon must not allow compression or must only allow compression after successful authentication.

If compression is allowed in an SSH connection prior to authentication, vulnerabilities in the compression software could result in compromise of the system from an unauthenticated connection, potentially with root privileges.

From an ESXi shell, run the following command:

# /usr/lib/vmware/openssh/bin/sshd -T|grep compression

Expected result:

compression no

If the output does not match the expected result, this is a finding.

From an ESXi shell, add or correct the following line in "/etc/ssh/sshd_config":

Compression no