The Oracle Linux operating system must be configured so that the SSH daemon does not allow compression or only allows compression after successful authentication.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-221864 | OL07-00-040470 | SV-221864r991589_rule | CCI-000366 | 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 | |||
| Oracle Linux 7 Security Technical Implementation Guide | 2025-05-08 | |||
Details
Check Text (C-221864r991589_chk)
Note: For Oracle Linux 7.4 and above, this requirement is not applicable.
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 returned line is commented out, this is a finding.
Fix Text (F-23568r880590_fix)
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.