MAIL-8818 - Postfix information leakage

(Mail)

This information is provided as part of the Lynis community project. It is related to Lynis control MAIL-8818 and should be considered as-is and without guarantees. Any advice and commands should be tested before implementing them in production environments.

Description

To prevent announcing software or version to malicious people or scripts, it is advised to hide such information.

How to solve

It is common to see that software display their version number, name, or other details. While it may look innocent, it is a form of information leakage. It may provide attackers too much information during their reconnaissance phase, in which they try to determine what software is running. Especially when sharing software names together with the version, it becomes much easier to target that software.

For Postfix it is common to see it that it is running Postfix. Therefore change the "smtpd_banner" in main.cf and restart the daemon. The banner could be as simple as showing only "$myhostname ESMTP", to indicate this is a mail server, without revealing other details. The hostname is a required part of the standard, and easy to determine anyways.

Additional resources

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Lynis is a technical security auditing tool for Unix flavors like Linux, macOS, AIX, Solaris, and *BSD. It is open source software and free to use. Typical usage include system hardening, compliance testing, and vulnerability scanning. The project has an active community, including development via GitHub.

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