Executive brief
genieacs-mcp is a bridge tool that exposes GenieACS CPE management operations through a local HTTP interface. In its default configuration, it listens on localhost without authentication. A malicious website can exploit DNS rebinding to trick a victim's browser into making requests to the local listener while using the attacker's origin, allowing the attacker to perform CPE operations (device reboot, firmware updates, configuration changes, tag management) through the victim's GenieACS backend without any authentication or authorization check.
Technical details
The vulnerability is a missing Host/Origin validation flaw in the Streamable HTTP MCP transport. When genieacs-mcp runs in HTTP mode on localhost (the documented default with no MCP_AUTH_TOKEN set), the server accepts requests with arbitrary Host and Origin headers and does not validate them before processing MCP operations. An attacker can perform DNS rebinding to direct a victim's browser to 127.0.0.1:8080 while maintaining the attacker's origin header in the HTTP request. This bypasses the intended loopback-only security model. The affected code is in cmd/server/main.go:92–109, where the unauthenticated branch creates an HTTP server without Host/Origin validation middleware. The attack requires network reachability to the victim's loopback interface (via DNS rebinding and browser-originating requests), no authentication is needed for the default loopback config, and an attacker can invoke any MCP tool exposed by the server (get_parameter, set_parameter, reboot_device, download_firmware, etc.). Versions <= 0.3.1 are affected; version 0.3.2 includes a fix.
Affected products
- GenieACS genieacs-mcp <= 0.3.1
Timeline
- 2026-06-15: disclosed: GitHub advisory published
- 2026-08-25: advisory: Advisory updated
- 2026-<UNKN: patched: Fix released in version 0.3.2
References
- https://api.github.com/users/avishaigonen-pluto
- https://github.com/avishaigonen-pluto
- https://api.github.com/users/avishaigonen-pluto/gists%7B/gist_id%7D
- https://api.github.com/users/avishaigonen-pluto/repos
- https://avatars.githubusercontent.com/u/290662811?v=4
- https://api.github.com/users/avishaigonen-pluto/events%7B/privacy%7D