Censys vs Microsoft Security Response Center (MSRC)

Censys grew out of the University of Michigan's ZMap internet-scanning research and now re-scans the full public IPv4 space multiple times a day, fingerprinting open ports, services, and TLS certificates. Its Search API exposes that host and certificate-transparency dataset for asset discovery, exposure monitoring, and threat hunting, and underpins Censys's own attack-surface-management product. Access is account-scoped through an API key, with a limited free community tier and metered paid plans for higher query volume.

MSRC's CVRF API serves Microsoft's own machine-readable security-update bulletins: list every bulletin's ID and dates from `/updates`, then pull one full document by ID (e.g. "2026-Jan") from `/cvrf/{id}` -- as CVRF XML by default, or the same CVRF document serialised to JSON under an `Accept: application/json` header. It's a fully public, unauthenticated REST endpoint with no signup or key required, backing tools like the community MsrcSecurityUpdates PowerShell module. Two traps confirmed live: the OData-shaped response envelope is misleading (most `$filter`/`$top` syntax 500s, and there's no CVE-to-bulletin lookup at all), and the separately documented `/csaf/{id}` route rejected all 17 id formats probed with "Invalid ID format" -- so despite the CSAF branding, the JSON this API actually returns is CVRF, not CSAF. The old stored URL pointed at the unrelated Report Abuse API's developer page; the live developer portal for this security-updates API now redirects straight to its published OpenAPI/Swagger definition.