CVE-2026-16584: AWS API MCP Server security policy bypass via startup initialization failure

Primary-source research dossier for CVE-2026-16584 (AWS API MCP Server Security Policy Bypass via Startup Failure). AWS Security Bulletin 2026-063-AWS states that awslabs.aws-api-mcp-server versions >=0.2.13 and <1.3.47 load the read-operations index used by the optional security policy at startup; if initialization fails, the server continues running with per-request policy checks skipped for the lifetime of the process. In vulnerable versions, a configured denyList or elicitList can therefore be bypassed and denied/gated AWS CLI operations may reach the downstream AWS-call boundary even though policy would normally block them. The patched release 1.3.47 fails closed: the server refuses to start when the read-operations index cannot be loaded, and request-time execution is denied when the index is unavailable. Evidence sources: AWS bulletin 2026-063-AWS, PyPI 1.3.47 release page, and awslabs/mcp commit ab1bbebc097d674c1cdd4bd75a8f313be18473bf. Repo-scoped project: awslabs/mcp.