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EUVD-2026-369695

2026-10-07T22:42:27.999065+00:00

EUVD-2026-369695

fkie_cve-2026-59973

2026-10-07T22:42:27.999102+00:00

FrontMCP is a TypeScript-first framework for the Model Context Protocol (MCP). From mcp-from-openapi 2.3.0 until 2.5.0 and from frontmcp and @frontmcp/adapters 1.2.1 until 1.5.0, libs/adapters/src/openapi/openapi.adapter.ts loadOpenAPISpec() forwards untrusted OpenAPI url and spec inputs and loadOptions.refResolution to OpenAPIToolGenerator.fromURL() and OpenAPIToolGenerator.fromJSON(). The external $ref guard checks parsed hostname strings without resolving addresses, pinning validated addresses, revalidating redirect targets, or normalizing IPv4-mapped IPv6. An authenticated user who can import or configure an OpenAPI specification in a hosted or multi-user deployment can use DNS-to-loopback resolution, redirect-to-loopback behavior, or IPv4-mapped IPv6 loopback forms to cause backend-origin requests to internal services. This can expose internal administrative APIs, metadata-like services, and other private network endpoints. The practical impact is lower when only a trusted local administrator can configure OpenAPI specs, and disabling external reference protocols prevents the external $ref request. This issue is fixed in mcp-from-openapi 2.5.0 and frontmcp and @frontmcp/adapters 1.5.0.

GHSA-65h7-9wrw-629c — FrontMCP and mcp-from-openapi have bypass of OpenAPI external $ref SSRF fix

2026-10-07T22:42:27.999141+00:00

Affected: npm: mcp-from-openapi, npm: @frontmcp/adapters, npm: frontmcp

## Summary

The published fix for GHSA-v6ph-xcq9-qxxj / CVE-2026-39885 added a direct hostname denylist for OpenAPI external `$ref` dereferencing, but the latest patched dependency `mcp-from-openapi` 2.3.0 still makes backend-origin requests to loopback when the target is reached through hostname resolution, redirects, or IPv4-mapped IPv6 syntax.

FrontMCP latest release v1.2.1 and current main still call `OpenAPIToolGenerator.fromURL()` and `OpenAPIToolGenerator.fromJSON()` from `mcp-from-openapi` 2.3.0 when loading OpenAPI adapters. An attacker who can cause a hosted or multi-user FrontMCP deployment to load an untrusted OpenAPI spec can trigger requests from the server to localhost or private services during tool generation.

This is a latest-version bypass of the previous fix. A direct `http://127.0.0.1` `$ref` control is now denied and produces zero canary hits, while semantically equivalent loopback targets still reach the canary.

## Latest versions checked

- `frontmcp` npm latest: 1.2.1 - `@frontmcp/adapters` npm latest: 1.2.1 - `mcp-from-openapi` npm latest: 2.3.0 - FrontMCP release tag: v1.2.1, commit db323976c66297d684a3e63bbfe1db6b310f2944 - FrontMCP current main checked: c15b79abe8c6a3cb71d4b7a3bafb8190730dc756

The release tag and current main both keep `mcp-from-openapi` 2.3.0 in `package.json` and `libs/adapters/package.json`, and both keep the OpenAPI adapter forwarding untrusted `url`, `spec`, and `loadOptions.refResolution` into `OpenAPIToolGenerator`.

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