CVE-2026-55637 genieacs-mcp: DNS rebinding reaches local GenieACS MCP Streamable HTTP transport
Attacker uses DNS rebinding to access local MCP server, exposing or modifying GenieACS CPE management state via unauthenticated HTTP listener.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-55637?
CVE-2026-55637 is a high-severity server-side request forgery vulnerability in GeiserX genieacs-mcp, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-346
Which versions are affected by CVE-2026-55637?
3 open source packages ship an affected version, including github.com/geiserx/genieacs-mcp.
| Package | Affected | Fixed in |
|---|---|---|
github.com/geiserx/genieacs-mcp Go | All versions | 0.3.2 |
github.com/geiserx/genieacs-mcp Go | All versions | 0.3.2 |
github.com/geiserx/genieacs-mcp Go | All versions | 0.3.2 |
How do I fix CVE-2026-55637?
Upgrade github.com/geiserx/genieacs-mcp to 0.3.2 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-55637 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55637 exists.
Sources
Also known as GHSA-cmwv-wf9p-p8wx, GO-2026-6295.