# 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.

- **Severity:** High 8.8 (`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`)
- **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:** Yes
- **Published:** 25 Aug 2026
- **Updated:** 25 Aug 2026
- **Also known as:** GHSA-cmwv-wf9p-p8wx, GO-2026-6295

## 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 (Origin Validation Error)

## Which versions are affected by CVE-2026-55637?

3 open source packages ship an affected version, including github.com/geiserx/genieacs-mcp.


| Package | Ecosystem | 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.

## Is CVE-2026-55637 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55637 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55637 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-55637 exists.

Affected packages and fixed versions:
- github.com/geiserx/genieacs-mcp (Go): affected all versions; fixed in 0.3.2
- github.com/geiserx/genieacs-mcp (Go): affected all versions; fixed in 0.3.2
- github.com/geiserx/genieacs-mcp (Go): affected all versions; fixed in 0.3.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-55637/ (Markdown: https://insights.sbomify.com/CVE-2026-55637/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55637
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55637
- OSV: https://osv.dev/vulnerability/CVE-2026-55637

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-55637/
Summaries are generated and may contain mistakes; the official description above is the record.