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The SSH daemon must not allow compression or must only allow compression after successful authentication.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
|---|---|---|---|---|
| V-75851 | UBTU-16-030350 | SV-90531r2_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 |
|---|---|
| Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide | 2018-07-18 |
Details
| Check Text ( C-75539r1_chk ) |
|---|
| 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 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-82481r3_fix) |
|---|
| Configure SSH to use 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 daemon must be restarted for the changes to take effect. To restart the SSH daemon, run the following command: # sudo systemctl restart sshd.service |