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The Ubuntu operating system must be configured to prevent unrestricted mail relaying.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
|---|---|---|---|---|
| V-75891 | UBTU-16-030620 | SV-90571r2_rule | Medium |
| Description |
|---|
| If unrestricted mail relaying is permitted, unauthorized senders could use this host as a mail relay for the purpose of sending spam or other unauthorized activity. |
| STIG | Date |
|---|---|
| Canonical Ubuntu 16.04 LTS Security Technical Implementation Guide | 2018-07-18 |
Details
| Check Text ( C-75579r2_chk ) |
|---|
| Determine if "postfix" is installed with the following commands: Note: If postfix is not installed, this is Not Applicable. # dpkg -l | grep postfix ii postfix 3.1.0-3 Verify the Ubuntu operating system is configured to prevent unrestricted mail relaying. If postfix is installed, determine if it is configured to reject connections from unknown or untrusted networks with the following command: # postconf -n smtpd_client_restrictions smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject If the "smtpd_relay_restrictions" parameter contains any entries other than "permit_mynetworks", "permit_sasl_authenticated" and "reject", is missing, or is commented out, this is a finding. |
| Fix Text (F-82521r2_fix) |
|---|
| If "postfix" is installed, modify the "/etc/postfix/main.cf" file to restrict client connections to the local network with the following command: # sudo postconf -e 'smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject' |