Look up a CVE by id (e.g. CVE-2021-44228) across three authoritative vulnerability feeds in one call. Query: cve (CVE-YYYY-NNNN). Returns the canonical record — description, CVSS base score + severity + vector, CWE weakness ids, published/modified dates, reference links — plus whether it is on the US CISA Known Exploited Vulnerabilities catalog (with remediation due date and known-ransomware flag) and its EPSS exploit-probability score and percentile. The exploited and EPSS sections report independently, so one feed being unavailable does not fail the call. 404 if the CVE id is unknown. For triage, prioritization, and anti-hallucination on vulnerability claims.