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


Finding ID Version Rule ID IA Controls Severity
V-256390 ESXI-70-000021 SV-256390r885951_rule Medium
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.
VMware vSphere 7.0 ESXi Security Technical Implementation Guide 2023-06-21


Check Text ( C-60065r885949_chk )
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.
Fix Text (F-60008r885950_fix)
From an ESXi shell, add or correct the following line in "/etc/ssh/sshd_config":

Compression no