Path Traversal Vulnerability in FastMCP API by PrefectHQ
CVE-2026-32871

10CRITICAL

Key Information:

Vendor

Prefecthq

Status
Fastmcp
Vendor
CVE Published:
2 April 2026

What is CVE-2026-32871?

In FastMCP, a vulnerability exists in the OpenAPIProvider prior to version 3.2.0, where the _build_url() method in the RequestDirector class fails to properly URL-encode path parameters when constructing HTTP requests. This oversight leads to potential path traversal attacks, allowing an attacker to manipulate the URL and access unauthorized backend endpoints. The issue can result in SSRF (Server-Side Request Forgery) since requests are sent with the authorization headers of the MCP provider. This vulnerability has been addressed in version 3.2.0.

Affected Version(s)

fastmcp < 3.2.0

References

https://github.com/PrefectHQ/fastmcp/security/advisories/...
x_refsource_CONFIRM
https://github.com/PrefectHQ/fastmcp/pull/3507
x_refsource_MISC
https://github.com/PrefectHQ/fastmcp/commit/40bdfb6b1de0c...
x_refsource_MISC

CVSS V4

Score:
10
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.