{"id":"CVE-2026-76169","title":"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","summary":"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 in…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N","cwe":["CWE-288","CWE-289"],"vendor":"fastify","product":"fastify","affected":["fastify >= 4.0.0, < 5.12.2"],"patched":["fastify 5.12.2"],"published":"2026-09-04","updated":"2026-09-15","sourceUpdated":"2026-09-15T20:07:46.700","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-76169","references":[{"url":"https://cna.openjsf.org/security-advisories.html","label":"ce714d77-add3-4f53-aff5-83d477b104bb"},{"url":"https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7","label":"ce714d77-add3-4f53-aff5-83d477b104bb"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-76169.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-76169"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2528456"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-76169"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-76169"},{"url":"https://github.com/fastify/fastify/commit/93c239a380f3f2778bb7565fcdf777e91cfe1fbc"},{"url":"https://github.com/fastify/fastify/releases/tag/v5.12.2"},{"url":"https://github.com/advisories/GHSA-p68q-wchp-6fh7"},{"url":"https://access.redhat.com/errata/RHSA-2026:84734"}],"tags":["nvd","csaf","vex","red-hat","ghsa","npm"],"epss":0.0053,"epssPercentile":0.44634,"ingestedAt":"2026-09-08T19:08:49.592Z","aliases":["GHSA-p68q-wchp-6fh7"],"ecosystem":"npm","slug":"CVE-2026-76169","body":"## Overview\n\nfastify 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.\n\n## Affected\n\n- `fastify >= 4.0.0, < 5.12.2`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `fastify 5.12.2`\n\n## Vendor advisories\n\n- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux AI (RHEL AI) 3, Red Hat OpenShift AI (RHOAI), Red Hat OpenShift Dev Spaces · no fix planned: Red Hat Enterprise Linux AI (RHEL AI) 3, Red Hat OpenShift AI (RHOAI), Red Hat OpenShift Dev Spaces · updated 2026-10-19 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-76169.json)\n- **RHSA-2026:84734** · Red Hat · fixed in: Red Hat OpenShift AI 3.4 · released 2026-10-19 · [advisory](https://access.redhat.com/errata/RHSA-2026:84734)\n\n## Package advisory (CVE-2026-76169)\n\nAffected packages:\n\n- `fastify >= 4.0.0, < 5.12.2`\n\nPatched in:\n\n- `fastify 5.12.2`\n\nSource: https://github.com/advisories/GHSA-p68q-wchp-6fh7","depth":"twilight","depthScore":41,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}