API Versioning

API versioning enables organizations to evolve their APIs without breaking existing client integrations. Common versioning strategies include URI path versioning (e.g., /v1/users), query parameter versioning, custom header versioning, and content negotiation via the Accept header. Each approach has trade-offs in terms of simplicity, cacheability, and client impact.

From a security perspective, API versioning introduces important considerations. Older API versions may contain known vulnerabilities that have been fixed in newer versions but remain exploitable in the deprecated endpoints. If legacy versions are not properly maintained or decommissioned, they become a growing attack surface. Attackers often target older API versions specifically because they are less likely to have current security patches and monitoring.

Best practices for secure API versioning include establishing a clear deprecation timeline and communicating it to consumers, applying security patches to all supported versions simultaneously, implementing monitoring and alerting on deprecated version usage, eventually sunsetting old versions by returning appropriate HTTP status codes such as 410 Gone, and ensuring that security controls like authentication and rate limiting are consistently applied across all versions. Organizations should also avoid versioning internal APIs unnecessarily and should use contract testing to verify that security controls remain intact when introducing new versions. A version inventory should be maintained as part of the API security program.