The correct action for the Scrum Master is to add a Product Backlog item to address the security issue. This approach ensures that the risk is formally tracked and prioritized appropriately within the backlog, following Scrum practices. By doing this, the issue receives proper attention and can be handled in a structured manner during sprint planning. Notifying the test team, asking the Development Team member to share the issue, or waiting until the Sprint Retrospective are less effective in ensuring that the security risk is addressed systematically.