MCP Security 2025 — How to Safely Aggregate Multiple Servers Behind One Endpoint

TL;DR: Treat every MCP server as untrusted by default. Enforce project‑level allowlists, per‑server credentials, strict SSE streaming rules, and durable audits. Host the router on the edge but store policy in a serverless Postgres (like Neon). See Governance, Auth, and Observability posts linked below for deep dives.

Who this is for and intent

• Audience: Staff engineers, platform teams, and security leads adopting the Model Context Protocol (MCP) at scale.
• Intent: Know — a prescriptive security baseline for a single MCP endpoint that aggregates many servers.

Table of contents

• What changed in 2024–2025 for MCP adoption
• Threat model for a multi‑server MCP router
• Controls that matter now (checklist)
• Hosting pattern: Workers + Neon
• Example: secure SSE relay code
• Performance & UX tips
• Related posts and further reading

What changed in 2024–2025 for MCP

• MCP became a widely referenced standard for connecting AI apps to tools and data. Anthropic positions it as the “USB‑C of AI apps,” with first‑party docs and examples. See Anthropic’s MCP docs. Source. citeturn0search1
• Microsoft announced broad first‑party MCP support across Windows, GitHub, and Azure at Build 2025, accelerating enterprise adoption. Source. citeturn1search0

Threat model for a multi‑server router

• Untrusted servers: You connect many third‑party servers; each tool may over‑reach or leak sensitive data if unconstrained.
• Streaming surfaces: Event injection or oversized chunks can destabilize clients if streams aren’t validated.
• Supply chain: Unpinned server versions and unsigned artifacts raise tampering risk.

Controls that matter now (baseline)

1. Default‑deny and allowlists
   • Per project, enumerate allowed tools and servers. New servers/tools ship disabled until reviewed. Grounded in MCP’s open ecosystem; you must add your own policy gate. Anthropic MCP. citeturn0search1
2. Per‑server credentials and least privilege
   • Never reuse tokens across servers. Store issuer, scopes, and expiry; rotate and revoke centrally. See our Auth post.
3. SSE hygiene at the edge
   • Only pass through text/event-stream. Validate event names, cap chunk sizes, and add heartbeats. Cloudflare’s EventSource and Streams docs show the primitives. EventSource, Streams. citeturn0search2turn7search0
4. Auditing and rate limits
   • Log project, tool, status, duration, and byte counts. Apply per‑tool budgets; trip circuit breakers on repeated failures. Cloudflare Rate Limiting runs close to the request path. Docs. citeturn7search5
5. Supply‑chain hardening
   • Pin versions; verify builds with Sigstore Cosign and adopt SLSA levels for provenance. Cosign, SLSA. citeturn5search0

Hosting pattern: Workers + Neon

• Use Cloudflare Workers for low‑latency routing/streaming and Neon for durable policy/audit storage with the serverless driver. Workers↔Neon, Neon serverless driver. citeturn0search0turn0search7

Example: secure SSE relay (sketch)

Performance & UX

• Aim for TTFT < 500ms on short tool runs. Stream early; flush heartbeats every 15s to keep intermediaries happy. Use Smart Placement to run near your DB if needed. Smart Placement. citeturn7search7

Related posts (topic cluster)

• Auth for MCP Routers — API keys, OAuth device code → 09 (Buy/Do)
• Governance Playbook — registries, approvals, signatures → 05 (Know)
• Observability — OpenTelemetry at the edge → 10 (Know)

Outbound sources

• Anthropic MCP overview. docs.anthropic.com
• Cloudflare EventSource & Streams. developers.cloudflare.com
• Neon + Workers. developers.cloudflare.com
• Microsoft Build 2025 (MCP on Windows, ecosystem). blogs.microsoft.com

Call to action

• Get our Security Checklist PDF and a sample wrangler.toml policy starter. Or set up a demo of routermcp.

FAQ Q: Is SSE required for MCP?
A: No. MCP defines how tools are exposed/invoked, not transport. We recommend SSE for incremental results in browser/edge runtimes. See MDN SSE and Cloudflare EventSource docs. MDN, Cloudflare. citeturn2search3turn0search2

Q: Where should I store audits? A: Keep immutable rows in Postgres with minimal PII. Neon’s serverless driver works with Workers. Neon driver. citeturn0search7

Q: How do I stop a misbehaving tool? A: Trip a circuit breaker, block the tool in the allowlist, and revoke its token. Rate‑limit at the edge to dampen retries. Rate limiting. citeturn7search5

SEO schema

Summary

• One endpoint can be safe if you default‑deny, scope credentials, validate streams, and audit precisely. Start with the checklist above, then deepen with our posts on Auth (09), Governance (05), and Observability (10).

Pre‑publish checklist (fast)

1. Intent (Know). 2) Title/meta aligned. 3) Short slug. 4) TL;DR present. 5) Unique code example added. 6) FAQ schema included. 7) 2–3 internal + 2–3 outbound links. 8) Images compressed; alt text done. 9) Readability pass. 10) CTA to get the checklist.