Moodle 3.1.17 release notes
From MoodleDocs
This version of Moodle is no longer supported for general bug fixes. You are encouraged to upgrade to a supported version of Moodle.
Releases > Moodle 3.1.17 release notes
Release date: 11 March 2019
Security issues
Details of any security issues will be released after a period of approximately one week to allow system administrators to safely update to the latest version.