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{}

{"analysis": {"en": {"generated_at": "2026-04-18T05:12:33.452979+00:00", "value": {"mitigation_remediation": ["Upgrade @fastify/middie to version 9.1.0 or later immediately.", "If upgrading is not yet possible, remove middie from routes that enforce critical access controls or add an additional authentication layer that operates after middie processing so that bypassed middleware does not grant access.", "Disable the use of percent\u2011encoding in protected path prefixes by normalizing incoming URLs before they reach middie, or configure your application to reject encoded characters in path segments until middie can process them."], "summary": {"action": "Immediate Patch", "impact": "Authentication Bypass / Unauthorized Access"}, "threat_synthesis": {"affected_systems": "The vulnerability affects all installations of the @fastify/middie plugin built before version 9.1.0, regardless of the Fastify core version. Users of the plugin should verify their package.json or lockfile to ensure the dependency is updated to v9.1.0 or later.", "description_and_impact": "@fastify/middie allows a middleware registered on a path prefix to be bypassed when an attacker uses URL\u2011encoded characters in that prefix, such as %61 for \"a\". The middleware engine incorrectly rejects the encoded path and skips execution, while the Fastify router decodes the URL and still delivers the intended route handler. This flaw permits attackers to reach endpoints that rely on middie middleware for authentication or authorization, effectively allowing unauthorized access without executing the protected logic. The weakness is classified as CWE\u2011177, fall\u2011through logic leading to an unintended code path.", "risk_and_exploitability": "With a CVSS score of 8.4 and an EPSS below 1%, the vulnerability is rated high severity but expected exploitation is currently low. It is not listed in the CISA KEV catalog, indicating no confirmed exploits yet. An attacker can exploit the flaw remotely by crafting a URL that includes a percent\u2011encoded character in a protected path prefix. No local privileges or specific configuration are required beyond having an exposed Fastify server that uses middie for route protection. The attack is straightforward and requires no authentication to initiate the request."}}}}, "created": "2026-01-20T08:43:34.212401+00:00", "updated": "2026-04-18T05:15:15.985239+00:00", "vendors": ["fastify", "fastify$PRODUCT$fastify"]}