{"id":"CVE-2026-112362","state":"PUBLISHED","title":"@fastify/express vulnerable to path-scoped middleware bypass via absolute-form request targets","description":"@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.","publishedAt":"2026-10-27T11:27:59.364Z","updatedAt":"2026-10-27T11:27:59.364Z","severity":{"score":9.1,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","source":"openjs"},"assigner":"openjs","products":["@fastify/express @fastify/express"],"affected":[{"vendor":"@fastify/express","product":"@fastify/express","packageURL":"pkg:npm/@fastify/express","defaultStatus":"unaffected","versions":[{"version":"4.0.5","status":"affected","lessThan":"4.0.9","versionType":"semver"},{"version":"4.0.9","status":"unaffected","versionType":"semver"}]}],"references":["https://github.com/fastify/fastify-express/security/advisories/GHSA-6h42-57hq-9746","https://cna.openjsf.org/security-advisories.html"],"weaknesses":["CWE-436"],"ingestedAt":"2026-10-29T20:10:43.281Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/112xxx/CVE-2026-112362.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-112362","state":"PUBLISHED","datePublished":"2026-10-27T11:27:59.364Z","dateUpdated":"2026-10-27T11:27:59.364Z","assignerShortName":"openjs","assignerOrgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateReserved":"2026-10-19T14:59:03.468Z"},"containers":{"cna":{"title":"@fastify/express vulnerable to path-scoped middleware bypass via absolute-form request targets","descriptions":[{"lang":"en","value":"@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."}],"affected":[{"vendor":"@fastify/express","product":"@fastify/express","packageURL":"pkg:npm/@fastify/express","defaultStatus":"unaffected","versions":[{"version":"4.0.5","status":"affected","lessThan":"4.0.9","versionType":"semver"},{"version":"4.0.9","status":"unaffected","versionType":"semver"}]}],"references":[{"url":"https://github.com/fastify/fastify-express/security/advisories/GHSA-6h42-57hq-9746"},{"url":"https://cna.openjsf.org/security-advisories.html"}],"metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","baseScore":9.1,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-436","lang":"en","description":"CWE-436: Interpretation Conflict","type":"CWE"}]}],"providerMetadata":{"shortName":"openjs","orgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateUpdated":"2026-10-27T11:27:59.364Z"},"credits":[{"lang":"en","type":"reporter","value":"agent-killjoy"},{"lang":"en","type":"remediation developer","value":"mcollina"},{"lang":"en","type":"remediation reviewer","value":"UlisesGascon"}],"x_generator":{"engine":"cve-kit 1.0.0"}}}}}