Description
@fastify/middie versions 9.1.0 through 9.3.2 decode the encoded slash %2F inside path parameter values before matching middleware paths, while Fastify's underlying router preserves the encoding during route lookup. The two layers disagree on the canonical request path, so the middleware fails to match a URL that the route handler does match. When middleware is used for authentication, authorization, rate limiting, or auditing on parameterized paths, an attacker can reach the protected handler by sending a single crafted URL with an encoded slash in the parameter position. The bypass is HTTP method agnostic and requires no authentication or special preconditions. Patches: upgrade to @fastify/middie 9.3.3. Workarounds: avoid parameterized middleware paths for security decisions, or enforce authentication at the route handler or via a Fastify hook that runs after the router has resolved the request.
Published: 2026-07-01
Score: 9.1 Critical
EPSS: n/a
KEV: No
Impact: n/a
Action: n/a
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History

Wed, 01 Jul 2026 12:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}


Wed, 01 Jul 2026 11:45:00 +0000

Type Values Removed Values Added
Description @fastify/middie versions 9.1.0 through 9.3.2 decode the encoded slash %2F inside path parameter values before matching middleware paths, while Fastify's underlying router preserves the encoding during route lookup. The two layers disagree on the canonical request path, so the middleware fails to match a URL that the route handler does match. When middleware is used for authentication, authorization, rate limiting, or auditing on parameterized paths, an attacker can reach the protected handler by sending a single crafted URL with an encoded slash in the parameter position. The bypass is HTTP method agnostic and requires no authentication or special preconditions. Patches: upgrade to @fastify/middie 9.3.3. Workarounds: avoid parameterized middleware paths for security decisions, or enforce authentication at the route handler or via a Fastify hook that runs after the router has resolved the request.
Title @fastify/middie vulnerable to authorization bypass via encoded slash in path parameter values
Weaknesses CWE-436
References
Metrics cvssV3_1

{'score': 9.1, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N'}


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cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-07-01T12:10:29.571Z

Reserved: 2026-06-30T09:12:37.009Z

Link: CVE-2026-14198

cve-icon Vulnrichment

Updated: 2026-07-01T12:10:20.482Z

cve-icon NVD

No data.

cve-icon Redhat

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cve-icon OpenCVE Enrichment

No data.

Weaknesses