CVE-2026-32871
- Source
- https://cve.org/CVERecord?id=CVE-2026-32871
- Import Source
- https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-32871.json
- JSON Data
- https://api.osv.dev/v1/vulns/CVE-2026-32871
- Aliases
- Downstream
- Published
- 2026-04-02T14:52:39.978Z
- Modified
- 2026-07-10T03:54:52.077284484Z
- Severity
-
- 10.0 (Critical) CVSS_V4 - 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 CVSS Calculator
- Summary
- FastMCP OpenAPI Provider has an SSRF & Path Traversal Vulnerability
- Details
-
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 buildurl() 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.
- Database specific
{ "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32871.json", "cna_assigner": "GitHub_M", "cwe_ids": [ "CWE-918" ] }- References
-
- https://github.com/PrefectHQ/fastmcp/releases/tag/v3.2.0
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-32871.json
- https://access.redhat.com/errata/RHSA-2026:36350
- https://access.redhat.com/security/cve/CVE-2026-32871
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32871.json
- https://github.com/PrefectHQ/fastmcp/security/advisories/GHSA-vv7q-7jx5-f767
- https://nvd.nist.gov/vuln/detail/CVE-2026-32871
- https://bugzilla.redhat.com/show_bug.cgi?id=2454434
- https://github.com/PrefectHQ/fastmcp/commit/40bdfb6b1de0ce30609ee9ba5bb95ecd04a9fb71
- https://github.com/PrefectHQ/fastmcp/pull/3507
Affected packages
Git / github.com/prefecthq/fastmcp
Affected ranges
- Type
- GIT
- Repo
- https://github.com/prefecthq/fastmcp
- Events
-
Introduced0 Unknown introduced commit / All previous commits are affectedFixedFixed
- Database specific
{ "source": [ "CPE_RANGE", "REFERENCES" ], "cpe": "cpe:2.3:a:jlowin:fastmcp:*:*:*:*:*:*:*:*", "extracted_events": [ { "introduced": "0" }, { "fixed": "3.2.0" } ] }