PLEASE DO NOT DISCLOSE SECURITY-RELATED ISSUES PUBLICLY, SEE BELOW.
October CMS is an evergreen product, no one version is singled out for security fixes because there is no way to update just one version. Builds are continually released and security fixes will always be available in the latest build.
If you discover a security vulnerability within October CMS, please send an email to the team at hello@octobercms.com. All security vulnerabilities will be promptly addressed.