A namespace monitoring service may track released namespaces such as internet protocol (IP) addresses and manage namespace cooldown pools, available namespace pools, and a registry of released namespaces to detect and mitigate security vulnerabilities that arise from reassignment of namespaces. The namespace monitoring service provides access to the released namespace registry and/or sends a data stream of namespace registry updates. The namespace monitoring service may manage namespace reassignment process and extend the cooldown period of released namespaces or place a hold on available name spaces.