{"id":"CVE-2026-84469","aliases":["GHSA-hwr6-493r-vm6h"],"url":"https://o3.security/vulnerability/CVE-2026-84469","summary":"fastify vulnerable to request validation bypass via skipped boolean false schemas","details":"### Impact\n\nFastify decided whether to validate a request part by checking its schema for JavaScript truthiness. JSON Schema Draft 7 defines the boolean `false` as a valid schema that rejects every instance, but because `false` is falsy, a route that set `body`, `querystring`, `params`, or `headers` to `false` had that part left uncompiled: no validator was attached and the request reached the handler. An application that used `false` as a deny-all schema to make a route unreachable was therefore fully bypassed, and an unauthenticated remote client could reach the handler with any input. The same applied to the documented `query` alias for `querystring`. This is a complete bypass rather than a weak-schema issue, since `false` is the strongest JSON Schema assertion and must always fail.\n\n### Patches\n\nRequest-part schemas are now selected by an explicit presence check rather than truthiness, so a boolean `false` (or `true`) schema is compiled and enforced, including through the `query` alias. Patched in fastify `5.12.2`. The fix is also included in the `6.0.0` release.\n\n### Workarounds\n\nIf upgrading is not immediately possible, express a deny-all request schema with an always-failing object schema instead of the boolean `false` (for example `{ \"not\": {} }`), or reject the request in an `onRequest` hook.","published":"2026-09-04T09:59:36.406Z","modified":"2026-10-21T03:00:29.549319298Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"fastify","fixedVersion":"5.12.2"}],"fix":{"url":"https://github.com/fastify/fastify/commit/7de6e81697778f9f41bd327a3b1c5c9a0d9637b4","label":"fastify/fastify@7de6e81"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84469.json"},{"type":"ADVISORY","url":"https://github.com/fastify/fastify/security/advisories/GHSA-hwr6-493r-vm6h"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-84469"},{"type":"WEB","url":"https://github.com/fastify/fastify/commit/7de6e81697778f9f41bd327a3b1c5c9a0d9637b4"},{"type":"PACKAGE","url":"https://github.com/fastify/fastify"},{"type":"WEB","url":"https://github.com/fastify/fastify/releases/tag/v5.12.2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T03:00:29.549319298Z"}}