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CVE-2026-125926 - Server-side request forgery in the server registration and update API in mcp-gateway-registry

Bulletin ID: 2026-180-AWS
Scope: AWS
Content Type: Important (requires attention)
Publication Date: 11/11/2026 13:00 PM PST


Description:

mcp-gateway-registry is an open-source registry and gateway for Model Context Protocol (MCP) servers that centralizes discovery, access control, and proxying of registered MCP tool assets. We identified CVE-2026-125926, a server-side request forgery issue in how the registry validates the upstream address of a registered server.

An authenticated user with permission to register or modify a server could configure an upstream address that caused the gateway to send requests to services on the deployment's internal network. In some cases the gateway returned those responses to the user.

Impacted versions: >= v1.0.3 AND <= 1.34.0

Resolution:

This issue has been addressed in mcp-gateway-registry version 1.35.0. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.

Note on version sequencing: a separate and unrelated issue in this product's external management API was addressed in version 1.25.0. A deployment running 1.25.0 or later carries that fix, but remains affected by the issue described here until it runs version 1.35.0 or later.

Post-upgrade actions:

Version 1.35.0 validates server upstream addresses when a server is registered or modified. It leaves server configurations stored before the upgrade unchanged. Customers who ran an affected version should take the following steps after upgrading:

  1. Review the upstream addresses of registered servers, and correct or remove any address you did not intend.
  2. Review application logs from the period an affected version was deployed for unexpected server registrations and changes.
  3. If the registry runs with an attached cloud role and the log review cannot rule out unexpected activity, review that role's activity and rotate its credentials.

Workarounds:

The following measures limit risk for deployments that cannot yet upgrade. They do not replace the post-upgrade actions above:

  • Limit the permission to register and modify servers to trusted accounts.
  • Restrict outbound network access from the registry and auth-server components to the destinations they need.
  • On Amazon EC2, require IMDSv2. Grant the role attached to each component only the permissions it needs.

References:

Acknowledgement:

We would like to thank the external researcher (handle novice-22) for collaborating on this issue through the coordinated disclosure process.


Please email aws-security@amazon.com with any s ecurity questions or concerns.