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CVE-2026-59973: CVE-2026-59973: High-Severity Server-Side Request Forgery in FrontMCP and mcp-from-openapi

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CVE-2026-59973: High-Severity Server-Side Request Forgery in FrontMCP and mcp-from-openapi

Vulnerability ID: CVE-2026-59973
CVSS Score: 8.5
Published: 2026-09-11

CVE-2026-59973 is a high-severity Server-Side Request Forgery (SSRF) vulnerability in FrontMCP and its underlying OpenAPI parsing library, mcp-from-openapi. The flaw allows authenticated attackers capable of importing or configuring OpenAPI specifications to bypass string-based hostname filtering mechanisms. By employing DNS wildcard loopbacks, HTTP redirects, or IPv4-mapped IPv6 address formatting, attackers can coerce the application into sending HTTP requests to internal networks, loopback adapters, and cloud metadata environments.

TL;DR

A validation bypass in FrontMCP and mcp-from-openapi allows authenticated users to execute arbitrary Server-Side Request Forgery (SSRF) attacks against internal interfaces, bypassing existing string-based denylists through DNS wildcards, HTTP redirects, or IPv4-mapped IPv6 addresses.

⚠️ Exploit Status: POC

Technical Details

  • CWE ID: CWE-918
  • Attack Vector: Network (AV:N)
  • CVSS Score: 8.5
  • Exploit Status: poc
  • KEV Status: Not Listed
  • Impact Type: Server-Side Request Forgery

Affected Systems

  • FrontMCP hosted tool generation services
  • Internal networks connected to FrontMCP containers
  • Cloud hosting platform metadata environments (IMDSv1/v2)
  • frontmcp: >= 1.2.1 < 1.5.0 (Fixed in: 1.5.0)
  • @frontmcp/adapters: >= 1.2.1 < 1.5.0 (Fixed in: 1.5.0)
  • mcp-from-openapi: >= 2.3.0 < 2.5.0 (Fixed in: 2.5.0)

Code Analysis

Commit: 96a78ea

Enforce secure defaults in frontmcp adapter configurations, including disabling external refs and limiting redirect actions.

Commit: be3409c

Introduce dynamic DNS validation module and enforce manual redirect validations inside the http resolver interface.

Exploit Details

  • Wiz Vulnerability Research Database: Validation testing confirming successful bypasses on mcp-from-openapi 2.3.0 using loopback canary tests with wildcards, redirects, and IPv4-mapped IPv6 formats.

Mitigation Strategies

  • Upgrade FrontMCP to version >= 1.5.0
  • Upgrade mcp-from-openapi to version >= 2.5.0
  • Disable external schema resolution via empty allowedProtocols rules
  • Implement network egress restrictions on container environments hosting FrontMCP

Remediation Steps:

  1. Review npm dependency tree for vulnerable versions of mcp-from-openapi (< 2.5.0) and frontmcp (< 1.5.0).
  2. Execute npm install frontmcp@1.5.0 or update package.json to point to fixed versions.
  3. Locate initialization files containing OpenapiAdapter.init and ensure refResolution.allowedProtocols is empty or locked to verified hosts.
  4. Deploy egress firewalls or network security groups to restrict outward container traffic to internal RFC 1918 networks.

References

Read the full report for CVE-2026-59973 on our website for more details including interactive diagrams and full exploit analysis.

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