Vulnerability · Published Sep 15, 2026 · Assigned by GitHub_M
CVE-2026-59973mcp-from-openapi: Bypass of OpenAPI external $ref SSRF fix in latest FrontMCP and mcp-from-openapi
High 8.5
In plain English
A high-severity server-side request forgery in frontmcp from agentfront. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 34% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| npm | @frontmcp/adapters | 1.5.0 | GHSA-65h7-9wrw-629c |
| npm | frontmcp | 1.5.0 | GHSA-65h7-9wrw-629c |
| npm | mcp-from-openapi | 2.5.0 | GHSA-65h7-9wrw-629c |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| agentfront | frontmcp | < 1.5.0 |
| agentfront | mcp-from-openapi | < 2.5.0 |
| @frontmcp | adapters | < 1.5.0 |
Weakness: CWE-918 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
References
- https://github.com/agentfront/frontmcp/security/advisories/GHSA-65h7-9wrw-629c x_refsource_CONFIRM
- https://github.com/agentfront/frontmcp/pull/496 x_refsource_MISC
- https://github.com/agentfront/mcp-from-openapi/pull/7 x_refsource_MISC
- https://github.com/agentfront/frontmcp/commit/96a78eaa5c6c4bc51cced557d83d1a03344cb03d x_refsource_MISC
- https://github.com/agentfront/mcp-from-openapi/commit/be3409cce6e97642696d4ee5a4e4e2712490b277 x_refsource_MISC
- https://github.com/agentfront/frontmcp/releases/tag/v1.5.0 x_refsource_MISC
- https://github.com/agentfront/mcp-from-openapi/releases/tag/v2.5.0 x_refsource_MISC