JRuby 10.0.x is the current version line for JRuby, and it will receive bug fixes and security updates.
The 9.4.x series is still being supported for security updates.
JRuby 9.3 is no longer supported; we recommend upgrading to JRuby 10. Users requiring JRuby 9.3 support may contact Headius Enterprises for commercial JRuby support offerings.
Please report vulnerabilities by emailing security@jruby.org. You can expect a response within 24 hours.