{"id":"CVE-2026-76169","sourceIdentifier":"ce714d77-add3-4f53-aff5-83d477b104bb","published":"2026-09-04T10:17:12.020","lastModified":"2026-09-15T20:07:46.700","vulnStatus":"Analyzed","cveTags":[],"descriptions":[{"lang":"en","value":"fastify versions >= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandler hook declared for that handler. The internal not-found router for encapsulated handlers dispatches malformed paths through a single shared handler pointer before URL decoding, ignoring the prefix and skipping the selected handler's normal lifecycle. An unauthenticated attacker can therefore reach an authentication-protected private fallback through an unrelated public prefix and read its full response, bypassing the authentication hook and breaking prefix encapsulation. Users should upgrade to fastify 5.12.2 or later."}],"affected":[{"source":"ce714d77-add3-4f53-aff5-83d477b104bb","affectedData":[{"vendor":"fastify","product":"fastify","defaultStatus":"unaffected","packageURL":"pkg:npm/fastify","versions":[{"version":"4.0.0","lessThan":"5.12.2","versionType":"semver","status":"affected"},{"version":"5.12.2","versionType":"semver","status":"unaffected"}]}]}],"metrics":{"cvssMetricV31":[{"source":"ce714d77-add3-4f53-aff5-83d477b104bb","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","baseScore":7.5,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"NONE","availabilityImpact":"NONE"},"exploitabilityScore":3.9,"impactScore":3.6}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-09-04T16:18:32.577097Z","id":"CVE-2026-76169","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"weaknesses":[{"source":"ce714d77-add3-4f53-aff5-83d477b104bb","type":"Secondary","description":[{"lang":"en","value":"CWE-288"}]}],"configurations":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:fastify:fastify:*:*:*:*:*:node.js:*:*","versionStartIncluding":"4.0.0","versionEndExcluding":"5.12.2","matchCriteriaId":"65C76641-6C57-4380-9FCA-50034F2ACDAC"}]}]}],"references":[{"url":"https://cna.openjsf.org/security-advisories.html","source":"ce714d77-add3-4f53-aff5-83d477b104bb","tags":["Third Party Advisory"]},{"url":"https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7","source":"ce714d77-add3-4f53-aff5-83d477b104bb","tags":["Mitigation","Vendor Advisory"]}]}