CVE-2026-55637: CWE-346: Origin Validation Error in GeiserX genieacs-mcp

The vulnerability in genieacs-mcp (prior to 0.3.2) involves the Streamable HTTP transport creating an unauthenticated listener on localhost without validating Host or Origin headers. This allows a malicious website to perform DNS rebinding attacks to send requests with attacker-controlled Host and Origin headers to the loopback listener. As a result, an attacker can initialize an MCP session and invoke management operations against the GenieACS NBI configured by ACS_URL. This can expose or modify device management state including reboots, firmware updates, parameter changes, and other device management tasks. The npm wrapper is unaffected because it does not expose an HTTP listener. The vulnerability is addressed in version 0.3.2.

Successful exploitation allows an attacker to bypass origin validation and perform unauthorized management operations on CPE devices managed by GenieACS. This includes exposing sensitive device management information and modifying device state such as triggering reboots, firmware tasks, parameter changes, and other provisioning operations. The vulnerability has a high severity with a CVSS 4.0 score of 8.8, indicating significant impact on confidentiality, integrity, and availability of managed devices.

This vulnerability is fixed in genieacs-mcp version 0.3.2. Users should upgrade to version 0.3.2 or later to remediate the issue. No other official remediation or temporary fixes are documented. The npm wrapper is not affected due to its use of a different transport mechanism. Patch status is not explicitly stated in the vendor advisory, but the fix is confirmed in version 0.3.2.