We support the most recent version of the software. Also, we support the last release before a new major version for a month (say, if v2.0.0 was the latest, we also support the latest v1 version and will backport bug fixes).
Please report vulnerabilities via email to security@axionspire.net or through GitHub's dedicated method (NOT using Issues). Include as detailed of a report as possible. We will reward researchers in a way outlined in our OSS Contributor Rewards program, possibly extending to money (though likely it will be in-game rewards, as this is a hobby project).