The SSH daemon must not allow compression or must only allow compression after successful authentication.

From VMware ESXi Server 5.0 Security Technical Implementation Guide

Associated with: CCI-000366

SV-51101r2_rule The SSH daemon must not allow compression or must only allow compression after successful authentication.

Vulnerability discussion

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.

Check content

Disable lock down mode. Enable the ESXi Shell. Execute the following command(s): # grep Compression /etc/ssh/sshd_config If the command returns nothing, or if the "Compression" attribute is set to "yes", this is a finding. Re-enable lock down mode.

Fix text

Disable lock down mode. Enable the ESXi Shell. Execute the following command(s): # vi /etc/ssh/sshd_config Add/modify the attribute line entry to the following (quotes for emphasis only): "Compression no" or "Compression delayed" Re-enable lock down mode.

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