CVE-2026-14198: critical vulnerability in @fastify/middie
@fastify/middie vulnerable to authorization bypass via encoded slash in path parameter values
Published
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.1epss 0.5%
@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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Affected products
@fastify/middie · @fastify/middieRelated CVEs — @fastify/middie
In the same product, most dangerous first.
CVE-2026-85184CRITICAL@fastify/middie vulnerable to path-scoped middleware bypass via absolute-form request targetEPSS 0.5%CVE-2026-14181HIGH@fastify/middie standalone engine vulnerable to Denial of Service via malformed percent-encoded pathsEPSS 0.5%CVE-2026-6270CRITICAL@fastify/middie vulnerable to middleware authentication bypass in child plugin scopesEPSS 0.5%CVE-2026-2880HIGH@fastify/middie has an improper path normalization vulnerabilityEPSS 0.4%CVE-2026-112712CRITICAL@fastify/middie vulnerable to path-scoped middleware bypass via scope prefix mismatchEPSS 0.3%CVE-2026-33804HIGH@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes optionEPSS 0.3%