The latest released version of the SDK is supported with security updates. You can find the latest version at: https://docs.canton.network/release-notes#release-notes
If you suspect that your issue has a security impact, do not use the issue tracker. In that case, please follow our responsible disclosure policy: https://www.digitalasset.com/responsible-disclosure and raise the Security Issue via the Security and Quality tab
To report an issue that does not have a security impact, open an issue on GitHub: https://github.com/digital-asset/dpm-assembly/issues/new
For general questions and/or support requests, please ask in our forum: https://forum.canton.network/