CVE-2026-59973
HighCVSS 8.5Summary
In mcp-from-openapi (2.3.0–2.5.0) and frontmcp and @frontmcp/adapters (1.2.1–1.5.0), loadOpenAPISpec() forwards untrusted OpenAPI URLs and inputs to the tool generator without proper destination validation. The external $ref guard only checks parsed hostname strings without resolving addresses, pinning validated addresses, revalidating redirects, or normalizing IPv4-mapped IPv6. An authenticated user able to import an OpenAPI specification can force requests to internal services.
Risk Assessment
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.
Recommendation
Update mcp-from-openapi to 2.5.0 and frontmcp and @frontmcp/adapters to 1.5.0. Consider disabling external reference protocols if not required.
Other vulnerabilities in FrontMCP
See all- CVE-2026-67531Critical
FrontMCP prior to 1.5.7 has a vulnerability in the codecall:execute tool that allows sandbox escape and remote code execution. By exploiting Zod objects, a script can access the Function constructor and execute arbitrary code in the server process. A single tools/call is sufficient to achieve full compromise.
- CVE-2026-39885High
The mcp-from-openapi library in FrontMCP prior to version 2.3.0 does not restrict $ref dereferencing in OpenAPI specifications, enabling SSRF and local file read attacks when processing untrusted specifications.
Original NVD description (English source)
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.