CVE-2026-59973

Vulnerability Description

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.

CVSS Score

Related Weaknesses (CWE)

References

• https://github.com/agentfront/frontmcp/commit/96a78eaa5c6c4bc51cced557d83d1a0334
• https://github.com/agentfront/frontmcp/pull/496
• https://github.com/agentfront/frontmcp/releases/tag/v1.5.0
• https://github.com/agentfront/frontmcp/security/advisories/GHSA-65h7-9wrw-629c
• https://github.com/agentfront/mcp-from-openapi/commit/be3409cce6e97642696d4ee5a4
• https://github.com/agentfront/mcp-from-openapi/pull/7
• https://github.com/agentfront/mcp-from-openapi/releases/tag/v2.5.0
• https://github.com/agentfront/frontmcp/security/advisories/GHSA-65h7-9wrw-629c