{"id":"CVE-2026-59973","state":"PUBLISHED","title":"mcp-from-openapi: Bypass of OpenAPI external $ref SSRF fix in latest FrontMCP and mcp-from-openapi","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.","publishedAt":"2026-09-15T15:13:40.053Z","updatedAt":"2026-09-16T16:06:53.148Z","severity":{"score":8.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["agentfront frontmcp","agentfront mcp-from-openapi","@frontmcp adapters"],"affected":[{"vendor":"agentfront","product":"frontmcp","versions":[{"version":"< 1.5.0","status":"affected"}]},{"vendor":"agentfront","product":"mcp-from-openapi","versions":[{"version":"< 2.5.0","status":"affected"}]},{"vendor":"@frontmcp","product":"adapters","versions":[{"version":"< 1.5.0","status":"affected"}]}],"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"],"weaknesses":["CWE-918"],"ingestedAt":"2026-10-29T20:12:32.778Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/59xxx/CVE-2026-59973.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-59973","state":"PUBLISHED","datePublished":"2026-09-15T15:13:40.053Z","dateUpdated":"2026-09-16T16:06:53.148Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-07-07T19:41:00.004Z"},"containers":{"cna":{"title":"mcp-from-openapi: Bypass of OpenAPI external $ref SSRF fix in latest FrontMCP and mcp-from-openapi","descriptions":[{"lang":"en","value":"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":[{"vendor":"agentfront","product":"frontmcp","versions":[{"version":"< 1.5.0","status":"affected"}]},{"vendor":"agentfront","product":"mcp-from-openapi","versions":[{"version":"< 2.5.0","status":"affected"}]},{"vendor":"@frontmcp","product":"adapters","versions":[{"version":"< 1.5.0","status":"affected"}]}],"references":[{"url":"https://github.com/agentfront/frontmcp/security/advisories/GHSA-65h7-9wrw-629c","name":"https://github.com/agentfront/frontmcp/security/advisories/GHSA-65h7-9wrw-629c","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/agentfront/frontmcp/pull/496","name":"https://github.com/agentfront/frontmcp/pull/496","tags":["x_refsource_MISC"]},{"url":"https://github.com/agentfront/mcp-from-openapi/pull/7","name":"https://github.com/agentfront/mcp-from-openapi/pull/7","tags":["x_refsource_MISC"]},{"url":"https://github.com/agentfront/frontmcp/commit/96a78eaa5c6c4bc51cced557d83d1a03344cb03d","name":"https://github.com/agentfront/frontmcp/commit/96a78eaa5c6c4bc51cced557d83d1a03344cb03d","tags":["x_refsource_MISC"]},{"url":"https://github.com/agentfront/mcp-from-openapi/commit/be3409cce6e97642696d4ee5a4e4e2712490b277","name":"https://github.com/agentfront/mcp-from-openapi/commit/be3409cce6e97642696d4ee5a4e4e2712490b277","tags":["x_refsource_MISC"]},{"url":"https://github.com/agentfront/frontmcp/releases/tag/v1.5.0","name":"https://github.com/agentfront/frontmcp/releases/tag/v1.5.0","tags":["x_refsource_MISC"]},{"url":"https://github.com/agentfront/mcp-from-openapi/releases/tag/v2.5.0","name":"https://github.com/agentfront/mcp-from-openapi/releases/tag/v2.5.0","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"NONE","baseScore":8.5,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"LOW","privilegesRequired":"LOW","scope":"CHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-918","lang":"en","description":"CWE-918: Server-Side Request Forgery (SSRF)","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-09-15T15:13:40.053Z"},"source":{"advisory":"GHSA-65h7-9wrw-629c","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/agentfront/frontmcp/security/advisories/GHSA-65h7-9wrw-629c","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-16T16:06:47.172118Z","id":"CVE-2026-59973","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-16T16:06:53.148Z"}}]}}}