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RHEL 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-258002 | RHEL-09-255130 | SV-258002r991589_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 |
|---|---|
| Red Hat Enterprise Linux 9 Security Technical Implementation Guide | 2024-06-04 |
Details
| Check Text ( C-61743r952199_chk ) |
|---|
| Verify the 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-61667r925992_fix) |
|---|
| Configure the SSH daemon to not allow compression. Uncomment the "Compression" keyword in "/etc/ssh/sshd_config" on the system 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 |