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

From Red Hat Enterprise Linux 7 Security Technical Implementation Guide

Associated with: CCI-000366

SV-86891r2_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

Verify the SSH daemon performs compression after a user successfully authenticates. Check that the SSH daemon performs compression after a user successfully authenticates with the following command: # grep -i compression /etc/ssh/sshd_config Compression delayed If the "Compression" keyword is set to "yes", is missing, or the retuned line is commented out, this is a finding.

Fix text

Uncomment the "Compression" keyword in "/etc/ssh/sshd_config" (this file may be named differently or be in a different location if using a version of SSH that is provided by a third-party vendor) on the system and set the value to "delayed" or "no": Compression no The SSH service must be restarted for changes to take effect.

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