The SSH client must be configured to not allow X11 forwarding.

From VMware ESXi Server 5.0 Security Technical Implementation Guide

Associated with: CCI-000366

SV-51087r2_rule The SSH client must be configured to not allow X11 forwarding.

Vulnerability discussion

X11 forwarding over SSH allows for the secure remote execution of X11-based applications. This feature can increase the attack surface of an SSH connection and should not be enabled unless needed.

Check content

Disable lock down mode. Enable the ESXi Shell. Check the SSH client configuration for the X11 forwarding setting. # grep -i "^ForwardX11" /etc/ssh/ssh_config If "ForwardX11" is set to "yes", this is a finding. If the /etc/ssh/ssh_config file does not exist or the ForwardX11 option is not set, this is not a finding. Re-enable lock down mode.

Fix text

Disable lock down mode. Enable the ESXi Shell. Edit the SSH client configuration and add/modify the "ForwardX11" configuration to "no". # vi /etc/ssh/ssh_config Re-enable lock down mode.

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