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

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
GEN005539-ESXI5-000113	GEN005539-ESXI5-000113	GEN005539-ESXI5-000113_rule		Medium

Description
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.

STIG	Date
VMware ESXi v5 Security Technical Implementation Guide	2013-01-15

Details

Check Text ( C-GEN005539-ESXI5-000113_chk )
Disable lock down mode. Enable the ESXi Shell. Login as root and execute the following command(s): # grep Compression /etc/ssh/sshd_config If the "Compression" is set to "yes" or "delayed", or the keyword/line is missing, this is a finding. Re-enable lock down mode.

Fix Text (F-GEN005539-ESXI5-000113_fix)
Disable lock down mode. Enable the ESXi Shell. Login as root and execute the following command(s): # vi /etc/ssh/sshd_config Add/modify the "Compression" keyword to "no", i.e.; Compression=no Re-enable lock down mode.