CVE-2026-22037

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{"affected": [{"affectedData": [{"product": "fastify-express", "vendor": "fastify", "versions": [{"status": "affected", "version": "< 4.0.3"}]}], "source": "security-advisories@github.com"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "The @fastify/express plugin adds full Express compatibility to Fastify. A security vulnerability exists in @fastify/express prior to version 4.0.3 where middleware registered with a specific path prefix can be bypassed using URL-encoded characters (e.g., `/%61dmin` instead of `/admin`). While the middleware engine fails to match the encoded path and skips execution, the underlying Fastify router correctly decodes the path and matches the route handler, allowing attackers to access protected endpoints without the middleware constraints. The vulnerability is caused by how @fastify/express matches requests against registered middleware paths. This vulnerability is similar to, but differs from, CVE-2026-22031 because this is a different npm module with its own code. Version 4.0.3 of @fastify/express contains a patch fort the issue."}, {"lang": "es", "value": "El plugin @fastify/express a\u00f1ade compatibilidad completa con Express a Fastify. Existe una vulnerabilidad de seguridad en @fastify/express anterior a la versi\u00f3n 4.0.3 donde el middleware registrado con un prefijo de ruta espec\u00edfico puede ser eludido utilizando caracteres codificados en URL (p. ej., '/%61dmin' en lugar de '/admin'). Mientras que el motor de middleware no logra coincidir con la ruta codificada y omite la ejecuci\u00f3n, el router subyacente de Fastify decodifica correctamente la ruta y coincide con el manejador de ruta, permitiendo a los atacantes acceder a puntos finales protegidos sin las restricciones del middleware. La vulnerabilidad es causada por c\u00f3mo @fastify/express compara las solicitudes con las rutas de middleware registradas. Esta vulnerabilidad es similar a, pero difiere de, CVE-2026-22031 porque este es un m\u00f3dulo npm diferente con su propio c\u00f3digo. La versi\u00f3n 4.0.3 de @fastify/express contiene un parche para el problema."}], "id": "CVE-2026-22037", "lastModified": "2026-06-17T10:19:24.147", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "LOW", "baseScore": 8.4, "baseSeverity": "HIGH", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "LOW", "scope": "CHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:L", "version": "3.1"}, "exploitabilityScore": 1.8, "impactScore": 6.0, "source": "security-advisories@github.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-22037", "options": [{"exploitation": "poc"}, {"automatable": "no"}, {"technicalImpact": "total"}], "role": "CISA Coordinator", "timestamp": "2026-01-20T21:34:36.586373Z", "version": "2.0.3"}}]}, "published": "2026-01-19T17:15:50.283", "references": [{"source": "security-advisories@github.com", "url": "https://github.com/fastify/fastify-express/commit/dc02a3fe1387f945143f22597baa42557d549a40"}, {"source": "security-advisories@github.com", "url": "https://github.com/fastify/fastify-express/security/advisories/GHSA-g6q3-96cp-5r5m"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Deferred", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-177"}, {"lang": "en", "value": "CWE-288"}], "source": "security-advisories@github.com", "type": "Secondary"}]}

{}

{"analysis": {"en": {"generated_at": "2026-04-18T05:11:14.599011+00:00", "value": {"mitigation_remediation": ["Update the @fastify/express package to version 4.0.3 or newer to incorporate the fix against URL\u2011encoding bypass.", "Verify that all middleware path prefixes are explicit and test that encoded URLs still trigger the intended middleware logic.", "Implement application\u2011level input validation or deploy a web application firewall that normalizes or rejects encoded URLs before they reach the application."], "summary": {"action": "Immediate Patch", "impact": "Unauthorized Access to Protected Endpoints"}, "threat_synthesis": {"affected_systems": "The issue affects the fastify:fastify\u2011express plugin in any Node.js application that uses @fastify/express version prior to 4.0.3. The vulnerability is present in every installation of the plugin that registers middleware with a specific path prefix before the patch is applied.", "description_and_impact": "A vulnerability in the @fastify/express plugin allows an attacker to bypass middleware that protects certain paths by sending URL\u2011encoded characters that the middleware engine does not match. The Fastify router decodes the path before routing, so a request such as \"/%61dmin\" matches the protected route without the middleware being executed. This flaw is an example of Improper Input Validation (CWE\u2011177) and Improper Check of Exception Response (CWE\u2011288), enabling attackers to gain unauthorized access to endpoints that are otherwise restricted.", "risk_and_exploitability": "The risk is high, with a CVSS score of 8.4, yet the EPSS score is very low (<1%), indicating limited current exploitation activity. It is not listed in the CISA KEV catalog. The likely attack vector is remote, where an attacker crafts HTTP requests containing URL\u2011encoded paths to reach protected endpoints. No special privileges or additional network access are required beyond the ability to send HTTP traffic to the vulnerable application."}}}}, "created": "2026-01-20T08:40:52.357242+00:00", "updated": "2026-04-18T05:15:15.983244+00:00", "vendors": ["fastify", "fastify$PRODUCT$fastify"]}