CVE-2026-55637
Received Received - Intake

Unauthenticated MCP Session Hijacking in GenieACS-MCP

Publication date: 2026-08-25

Last updated on: 2026-08-25

Assigner: GitHub, Inc.

Description
genieacs-mcp is an MCP server for GenieACS written in Go. Prior to 0.3.2, the Streamable HTTP transport in cmd/server/main.go creates an unauthenticated /mcp listener on the default MCP_LISTEN_ADDR value 127.0.0.1:8080 when MCP_AUTH_TOKEN is unset and the httpSrv.Start(addr) branch does not validate the Host or Origin headers. A malicious website can use DNS rebinding to send browser requests with attacker-controlled Host and Origin values to the loopback listener, initialize an MCP session, list tools, and invoke operations against the GenieACS NBI configured by ACS_URL. Successful exploitation can expose or modify CPE management state, including device reboots, firmware tasks, TR-069 parameter changes, presets, provisions, tags, connection requests, and task operations. The npm wrapper is not affected because it forces TRANSPORT=stdio and does not expose an HTTP listener. This issue is fixed in version 0.3.2.

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Meta Information

Published
2026-08-25
Last Modified
2026-08-25
Generated
2026-08-25
AI Q&A
2026-08-25
EPSS Evaluated
N/A
NVD
CVE-2026-55637
EUVD
EUVD-2026-65692

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
genieacs genieacs-mcp 0.3.2
geiserx genieacs_mcp to 0.3.2 (exc)
geiserx genieacs_mcp 0.3.2

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-346 The product does not properly verify that the source of data or communication is valid.

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Executive Summary

This vulnerability affects genieacs-mcp versions before 0.3.2. When the MCP_AUTH_TOKEN is not set, the Streamable HTTP transport creates an unauthenticated listener on 127.0.0.1:8080. A malicious website can use DNS rebinding to send requests with attacker-controlled Host and Origin headers to this listener, allowing unauthorized access to MCP session initialization, tool listing, and operation invocation against the GenieACS NBI.

Detection Guidance

Check if genieacs-mcp version is below 0.3.2 by running: genieacs-mcp --version. Verify if an unauthenticated /mcp listener is running on 127.0.0.1:8080 using netstat -tulnp | grep 8080 or ss -tulnp | grep 8080. Inspect network traffic for unexpected connections to localhost port 8080.

Impact Analysis

An attacker could exploit this to expose or modify CPE management state, including device reboots, firmware updates, TR-069 parameters, presets, provisions, tags, connection requests, and task operations. This could lead to unauthorized device control, data exposure, or service disruption in managed networks.

Compliance Impact

This vulnerability could lead to unauthorized access and modification of device management state, potentially exposing sensitive data or allowing control over connected devices. This may violate GDPR's data protection requirements and HIPAA's safeguards for protected health information if such data is managed or transmitted through affected systems.

Mitigation Strategies

Upgrade genieacs-mcp to version 0.3.2 or later. If upgrading is not possible, disable the HTTP listener by setting MCP_AUTH_TOKEN to a non-empty value or switch to the stdio transport. Block external access to 127.0.0.1:8080 using firewall rules.

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