{"id":"CVE-2026-76169","state":"PUBLISHED","title":"fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers","description":"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.","publishedAt":"2026-09-04T09:51:03.556Z","updatedAt":"2026-09-04T16:20:02.318Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","source":"openjs"},"assigner":"openjs","products":["fastify fastify"],"affected":[{"vendor":"fastify","product":"fastify","packageURL":"pkg:npm/fastify","defaultStatus":"unaffected","versions":[{"version":"4.0.0","status":"affected","lessThan":"5.12.2","versionType":"semver"},{"version":"5.12.2","status":"unaffected","versionType":"semver"}]}],"references":["https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7","https://cna.openjsf.org/security-advisories.html"],"weaknesses":["CWE-288"],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/76xxx/CVE-2026-76169.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-76169","state":"PUBLISHED","datePublished":"2026-09-04T09:51:03.556Z","dateUpdated":"2026-09-04T16:20:02.318Z","assignerShortName":"openjs","assignerOrgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateReserved":"2026-08-19T09:33:54.670Z"},"containers":{"cna":{"title":"fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers","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":[{"vendor":"fastify","product":"fastify","packageURL":"pkg:npm/fastify","defaultStatus":"unaffected","versions":[{"version":"4.0.0","status":"affected","lessThan":"5.12.2","versionType":"semver"},{"version":"5.12.2","status":"unaffected","versionType":"semver"}]}],"references":[{"url":"https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7"},{"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:N/A:N","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-288","lang":"en","description":"CWE-288: Authentication Bypass Using an Alternate Path or Channel","type":"CWE"}]}],"providerMetadata":{"shortName":"openjs","orgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateUpdated":"2026-09-04T09:51:03.556Z"},"credits":[{"lang":"en","type":"reporter","value":"vvvvvvvvvvitel"},{"lang":"en","type":"remediation developer","value":"mcollina"},{"lang":"en","type":"remediation reviewer","value":"UlisesGascon"},{"lang":"en","type":"finder","value":"schecthellraiser606"},{"lang":"en","type":"finder","value":"B1gN0Se"}],"x_generator":{"engine":"cve-kit 1.0.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-04T16:18:32.577097Z","id":"CVE-2026-76169","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-04T16:20:02.318Z"}}]}}}