{"id":"CVE-2026-112362","title":"@fastify/express vulnerable to path-scoped middleware bypass via absolute-form request targets","summary":"@fastify/express is a Fastify plugin that runs Express middleware inside Fastify. In versions 4.0.5 through 4.0.8, when Fastify runs with the non-default ignoreDuplicateSlashes option enabled, the plugin matches path-scoped Express middl…","severity":"critical","cvss":9.1,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","cvssSource":"cna","cwe":["CWE-436"],"vendor":"@fastify/express","product":"@fastify/express","affected":["@fastify/express >= 4.0.5 < 4.0.9"],"published":"2026-10-27","updated":"2026-10-27","sourceUpdated":"2026-10-27T11:27:59.364Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-112362","references":[{"url":"https://github.com/fastify/fastify-express/security/advisories/GHSA-6h42-57hq-9746"},{"url":"https://cna.openjsf.org/security-advisories.html"}],"tags":["cve.org"],"ingestedAt":"2026-10-27T16:11:59.306Z","slug":"CVE-2026-112362","body":"## Overview\n\n@fastify/express is a Fastify plugin that runs Express middleware inside Fastify. In versions 4.0.5 through 4.0.8, when Fastify runs with the non-default ignoreDuplicateSlashes option enabled, the plugin matches path-scoped Express middleware against a URL whose duplicate-slash normalization has also collapsed the separator after an absolute-form request target's scheme, so Fastify's router resolves the request to the scoped path and runs the handler while the Express layer no longer sees that path. As a result, a request using an absolute-form target can reach a handler on a scoped route such as an admin path while the middleware for authentication, authorization, or rate limiting is skipped. An unauthenticated attacker needs only the non-default ignoreDuplicateSlashes option to be enabled. The issue is fixed in @fastify/express 4.0.9, and users should upgrade to 4.0.9 or later. As a workaround, enforce authentication in a Fastify hook such as preHandler that runs after the router resolves the request, or leave ignoreDuplicateSlashes at its default.\n\n## Affected\n\n- `@fastify/express >= 4.0.5 < 4.0.9`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":50,"depthScoreParts":{"impact":50.1,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}