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.
- Postfix smtpd_banner option (Tips regarding configuring the smtpd_banner option)
Need more details?
Consider the upgrade to Lynis Enterprise to receive additional details and guidance. The Enterprise version helps to you with daily health checks of your environment, learn in-depth system hardening, and resources to protect your systems better.See demo
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.
Do you need to collect data from multiple systems or compliance reporting? Lynis Enterprise uses Lynis to collect the data and make your work easier.
Benefits: automate security audits, detailed reporting, compliance testing.
- Centralized management
- Improvement plan with priorities
- Predefined policies
- Integration (API)
- Improvement snippets for tools like Ansible, Chef, Cfengine, Puppet, and SaltStack