RHEL 9 SSH daemon must not allow compression or must only allow compression after successful authentication.
Severity | Group ID | Group Title | Version | Rule ID | Date | STIG Version |
|---|---|---|---|---|---|---|
| medium | V-258002 | SRG-OS-000480-GPOS-00227 | RHEL-09-255130 | SV-258002r991589_rule | 2025-02-27 | 2 |
| 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. |
| ℹ️ Check |
|---|
| 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 |
|---|
| 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 |