# CVE-2026-59973

## Summary

- **CVE ID:** CVE-2026-59973
- **Severity:** HIGH
- **CVSS Score:** 8.5 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N)
- **CWE:** CWE-918
- **Published:** Sep 15, 2026
- **Last Modified:** Sep 16, 2026

## 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 Products

- agentfront — frontmcp (< 1.5.0)
- agentfront — mcp-from-openapi (< 2.5.0)
- @frontmcp — adapters (< 1.5.0)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.38%
- **EPSS Percentile:** 31.3

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._