CVE-2026-112712: critical vulnerability in @fastify/middie
@fastify/middie vulnerable to path-scoped middleware bypass via scope prefix mismatch
Published · Updated
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.1epss 0.3%
@fastify/middie is the Express-style middleware engine for Fastify. In versions from 9.0.0 through 9.3.5, the use() function joined a path-scoped middleware's mount path to the plugin scope prefix in a way that could diverge from the path Fastify's router serves, most often when the scope prefix ended in a slash, and also for array mount paths and for mount paths written without a leading slash. When the two paths disagreed, the middleware was silently skipped while the route handler still ran, so path-scoped middleware such as authentication, authorization, or rate limiting could be bypassed by a single unauthenticated request. The issue is fixed in @fastify/middie 9.3.6, and users should upgrade to 9.3.6 or later. As a workaround, enforce authorization in a Fastify hook such as preHandler 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-2026-14198CRITICAL@fastify/middie vulnerable to authorization bypass via encoded slash in path parameter valuesEPSS 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-2026-33804HIGH@fastify/middie vulnerable to middleware bypass via deprecated ignoreDuplicateSlashes optionEPSS 0.3%