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High, CVSS 8.8amended

genieacs-mcp: DNS rebinding reaches local GenieACS MCP Streamable HTTP transport

CVE-2026-55637GHSA-cmwv-wf9p-p8wx

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/geiserx/genieacs-mcp 0.3.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
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 · score source
EPSS
  • CVE-2026-55637: 0.26% estimated exploitation activity in the next 30 days; percentile 18.43 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

genieacs-mcp exposes a local Streamable HTTP MCP endpoint that accepts attacker-controlled Host and Origin headers. A malicious web page can use DNS rebinding to route browser requests to a victim's loopback MCP listener while preserving the attacker origin. The server accepts the request, initializes an MCP session, lists GenieACS tools, and can invoke tools against the configured GenieACS NBI without a browser-supplied secret. The affected package is genieacs-mcp version 0.3.1 at commit 4d7d3c74740efb7f3833aadc8a8e9177650eb462. The vulnerable transport setup is in cmd/server/main.go. When TRANSPORT is not stdio, the server creates a Streamable HTTP MCP handler: For the default loopback listener, MCPAUTHTOKEN is not required. The unauthenticated branch calls httpSrv.Start(addr) directly. There is no middleware or MCP transport configuration that validates Host or Origin before /mcp handles the request. The README documents loopback HTTP as the default deployment mode and says…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 4 · amended ·

    Amended from ghsa record GHSA-cmwv-wf9p-p8wx

  2. Revision 3 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 2 · amended ·

    Amended from osv record GO-2026-6295

  4. Revision 1 · created ·

    Published from osv record GHSA-cmwv-wf9p-p8wx

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-55637

Advisory: genieacs-mcp: DNS rebinding reaches local GenieACS MCP Streamable HTTP transport
IDs: CVE-2026-55637, GHSA-cmwv-wf9p-p8wx
Record: https://patchnext.com/advisories/cve-2026-55637 (revision 4, source checked 26 Oct 2026, 15:28 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/geiserx/genieacs-mcp 0.3.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/geiserx/genieacs-mcp: affected <= 0.3.1; fixed in 0.3.2

## Suggested inspection (read-only)
- Go github.com/geiserx/genieacs-mcp: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/geiserx/genieacs-mcp.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-cmwv-wf9p-p8wx (OSV record GHSA-cmwv-wf9p-p8wx lists affected ranges: Go github.com/geiserx/genieacs-mcp >=0 <0.3.2 (fixed))
- Verified: https://osv.dev/vulnerability/GO-2026-6295 (OSV record GO-2026-6295 lists affected ranges: Go github.com/geiserx/genieacs-mcp >=0 <0.3.2 (fixed))
- Verified: https://github.com/advisories/GHSA-cmwv-wf9p-p8wx (GitHub-reviewed advisory GHSA-cmwv-wf9p-p8wx lists affected ranges: Go github.com/geiserx/genieacs-mcp >=0 <=0.3.1)

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