How should security teams measure whether MCP egress controls are working?

Why This Matters for Security Teams

MCP egress controls are only useful if they stop a server from reaching unapproved destinations at the moment the connection is made. That matters because MCP servers often act as tool routers, not static applications, and a permissive egress path can turn a single prompt or tool call into unexpected network reach. Security teams should measure the control against the actual destinations allowed by policy, not against whether a deny event was merely recorded. That distinction is central to how current guidance approaches agentic systems in the OWASP Agentic AI Top 10 and in NHIMG’s OWASP Agentic Applications Top 10 research. The practical risk is that teams stop at logging and assume containment is in place when the control is only observability. MCP environments also inherit identity and secret exposure issues that make egress validation more urgent. NHIMG’s State of Non-Human Identity Security shows how often organisations still lack confidence in controlling non-human access, which is exactly where outbound misuse becomes hard to detect. In practice, many security teams encounter weak MCP egress only after a server has already reached an internal service or metadata endpoint, rather than through intentional testing.

Related resources from NHI Mgmt Group

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