Fronteira: an MCP proxy that enforces policies against data exfiltration

What the research found

Fronteira is an MCP proxy that logs and enforces natural-language-derived policies on all MCP calls to block lethal-trifecta data exfiltration, with the author noting direct filesystem and internet access bypasses it.

Claims and how well the evidence supports them

1. Fronteira routes MCP tool calls through one proxy for logging and policy 98%
2. Natural-language rules compile to Guard DSL evaluated deterministically 92%
3. Direct filesystem, internet and API access bypasses Fronteira 98%
4. Uses JEV as a decision model for trade secret or medical content checks 98%

Evidence

• wiki.alcidesfonseca.com https://wiki.alcidesfonseca.com/blog/lessons-learned-building-fronteira

Actionability rated medium.