CVE-2026-55637: genieacs-mcp localhost endpoint permits DNS rebinding

Tracking: CVE-2026-55637
Severity: High

Who is affected

github.com/geiserx/genieacs-mcp through 0.3.1 using HTTP transport. The default listener is 127.0.0.1:8080; loopback binding alone does not remove the reported browser-origin attack.

How the attack works

The HTTP listener lacks the necessary authentication and Host/Origin validation for this scenario. A malicious webpage can use DNS rebinding to make browser requests reach the local MCP service, initialize a session, and invoke tools.

Those tools can act against the configured GenieACS northbound interface using the server's access. The consequences depend on available tools and privileges, including access to managed-device information and operations.

What to do

1. Upgrade to 0.3.2 or later and apply the project's HTTP authentication and host/origin protections.
2. Configure MCP_AUTH_TOKEN for HTTP access and verify unauthorized requests are rejected. Earlier behavior required the token only for non-loopback bindings.
3. Review unexpected tool activity and GenieACS actions. Restrict downstream permissions and avoid treating a localhost address as proof that only trusted applications can connect.

Scope and limits

The attack requires the browser and network conditions described in the advisory. It is not evidence that all local MCP servers are exposed in the same way.

Sources

• Original advisory or incident report