OL 9 SSH daemon must not allow compression or must only allow compression after successful authentication.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-271717 | OL09-00-002355 | SV-271717r1091863_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 |
| Oracle Linux 9 Security Technical Implementation Guide | 2025-05-08 |
Details
| Check Text (C-75767r1091861_chk) |
| Verify that OL 9 SSH daemon performs compression after a user successfully authenticates with the following command: $ sudo /usr/sbin/sshd -dd 2>&1 | awk '/filename/ {print $4}' | tr -d '\r' | tr '\n' ' ' | xargs sudo grep -iH '^\s*compression' 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-75674r1091862_fix) |
| Configure the SSH daemon to not allow compression. Add the following line to "/etc/ssh/sshd_config" or to a file in "/etc/ssh/sshd_config.d" or uncomment the line and set the value to "delayed" or "no": Compression no The SSH service must be restarted for changes to take effect: $ sudo systemctl restart sshd.service |