FrontMCP and mcp-from-openapi have bypass of OpenAPI external $ref SSRF fix

Published September 11, 2026 CVE-2026-59973

FrontMCP and mcp-from-openapi have bypass of OpenAPI external $ref SSRF fix. The published fix for GHSA-v6ph-xcq9-qxxj / CVE-2026-39885 added a direct hostname denylist for OpenAPI external $ref dereferencing, but the latest patched dependency mcp-from-openapi 2.3.0 still makes backend-origin requests to loopback when the target is reached through hostname resolution, redirects, or IPv4-mapped IPv6 syntax.

Severity
HighCVSS 8.5
Fix
Fixed in 2.5.0, 1.5.0Fix recorded today
Affected versions
2.3.0 or newer, but before 2.5.0; 1.2.1 or newer, but before 1.5.0; 1.2.1 or newer, but before 1.5.0
Affects
mcp-from-openapi+2 more

What to do

Run this in the application environment you want to check:

npm ls --all mcp-from-openapi @frontmcp/adapters frontmcp

Update to the fixed release for your version (2.5.0 or 1.5.0) or later.

Technical details

Affected software: mcp-from-openapi, @frontmcp/adapters, frontmcp

References

View Original Source