Bug fixes should ideally be handled in the same manner that other features are handled in the development cycle. Input DRs into the product backlog (for example, Jira issues) and prioritize them in the next sprint. In severe cases, exceptions can be made to stop new feature development and focus solely on closing a critical security flaw.
Incorporate regression testing after each DR is completed, to ensure that unintentional flaws are not introduced during the fix of the DR.