CVE-2026-77339: Process Compose: Browser DNS rebinding lets websites control local process-compose MCP tools

A malicious website can use DNS rebinding to control a developer’s local process-compose MCP SSE listener when MCP SSE is enabled. The vulnerable path accepts browser-origin requests before any Host validation, Origin validation, or caller-secret check, then dispatches the requests into process-compose MCP tools.

This advisory covers https://github.com/F1bonacc1/process-compose, confirmed at commit d56aa59df04b72f8644811ac581a051bec05e485.

The issue is in the MCP SSE transport, not the Gin REST API. The REST API token middleware protects REST routes, but the MCP listener is started separately and does not inherit that protection.