CVE-2026-32871Public exploitNetwork attack vector

SSRF via unencoded OpenAPI path parameters

Published Apr 2, 2026 · Updated Apr 2, 2026

SSRF in FastMCP before 3.2.0 allows remote attackers to access arbitrary backend endpoints through crafted OpenAPI path parameters. RequestDirector._build_url() substitutes path values without encoding before urljoin() normalizes traversal sequences outside the intended API prefix. Reachability requires an OpenAPIProvider route with attacker-controlled path parameters; resulting requests carry the provider's configured authorization headers.

CVSS severity10.0
Critical
EPSS probability0.91%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in FastMCP before 3.2.0 allows remote attackers to access arbitrary backend endpoints through crafted OpenAPI path parameters. RequestDirector._build_url() substitutes path values without encoding before urljoin() normalizes traversal sequences outside the intended API prefix. Reachability requires an OpenAPIProvider route with attacker-controlled path parameters; resulting requests carry the provider's configured authorization headers.

The record

CVE
CVE-2026-32871
Published
Apr 2, 2026
Updated
Apr 2, 2026
Vendor
Prefect Technologies, Inc.
Product
FastMCP
Classifications
CWE-918, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 2, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 2, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.2.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Prefect Technologies, Inc. · FastMCPversion=< 3.2.0

Published CVSS scores

10.0GitHub, Inc.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
8.5Red HatCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
10.0NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1190Exploit Public-Facing Application

Public exploit references

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Technologies

Your stack

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Your stack

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