{"cve":"CVE-2026-32871","nvd":{"published":"2026-04-02T15:16:38.740","modified":"2026-10-26T21:10:00.170","status":"Modified","description":"FastMCP is a Pythonic way to build MCP servers and clients. Prior to version 3.2.0, the OpenAPIProvider in FastMCP exposes internal APIs to MCP clients by parsing OpenAPI specifications. The RequestDirector class is responsible for constructing HTTP requests to the backend service. A vulnerability exists in the _build_url() method. When an OpenAPI operation defines path parameters (e.g., /api/v1/users/{user_id}), the system directly substitutes parameter values into the URL template string without URL-encoding. Subsequently, urllib.parse.urljoin() resolves the final URL. Since urljoin() interprets ../ sequences as directory traversal, an attacker controlling a path parameter can perform path traversal attacks to escape the intended API prefix and access arbitrary backend endpoints. This results in authenticated SSRF, as requests are sent with the authorization headers configured in the MCP provider. This issue has been patched in version 3.2.0.","cvss_v4":{"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H","score":10.0},"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H","score":10.0},"cwes":["CWE-918"],"references":["https://github.com/PrefectHQ/fastmcp/commit/40bdfb6b1de0ce30609ee9ba5bb95ecd04a9fb71","https://github.com/PrefectHQ/fastmcp/pull/3507","https://github.com/PrefectHQ/fastmcp/releases/tag/v3.2.0","https://github.com/PrefectHQ/fastmcp/security/advisories/GHSA-vv7q-7jx5-f767","https://access.redhat.com/errata/RHSA-2026:36350"],"products":["jlowin:fastmcp"],"source":"nvd","synced_at":"2026-10-26T21:38:48.864438205+00:00"},"epss":{"cve":"CVE-2026-32871","score":0.00909,"percentile":0.59705,"date":"2026-10-26"},"kev":null,"osv":[{"id":"GHSA-vv7q-7jx5-f767","url":"https://osv.dev/vulnerability/GHSA-vv7q-7jx5-f767","summary":"FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability","modified":"2026-09-10T03:50:41.271699069Z","packages":[{"ecosystem":"PyPI","name":"fastmcp","purl":"pkg:pypi/fastmcp","ranges":["<3.2.0"],"fixed":["3.2.0"]}]},{"id":"PYSEC-2026-338","url":"https://osv.dev/vulnerability/PYSEC-2026-338","summary":"FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability","modified":"2026-07-01T20:22:52.844800Z","packages":[{"ecosystem":"PyPI","name":"fastmcp","purl":"pkg:pypi/fastmcp","ranges":["<3.2.0"],"fixed":["3.2.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}