MCP Gateway: Authority-injection and JWT/session bypass via the unauthenticated router hair-pin "router-key" / "mcp-init-host" path — GHSA-G53W-W6MJ-HRPP

Summary

## Summary The MCP router (ext_proc) exposes an `initialize`-method code path that, when a request carries an `mcp-init-host` header, bypasses the gateway JWT session validator and rewrites the upstream `:authority` header to whatever the caller chooses, gated only by a single shared header value (`router-key`). The shared value is * a literal string (`secret-api-key`) baked into `cmd/mcp-broker-router/main.go` as…

Product

go: github.com/Kuadrant/mcp-gateway

What to do

General, cautious steps (verify details in the official source):

• Prioritize patching or mitigation immediately (treat as actively risky).
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source

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