{"cve":"CVE-2026-84504","nvd":{"published":"2026-09-04T10:17:13.790","modified":"2026-09-15T20:05:15.050","status":"Analyzed","description":"fastify versions before 5.12.2 treat the object resolved by a successful Ajv async validator as the value result protocol used by custom validator compilers. If a request that passes its route schema contains a property named value at the root, fastify replaces the entire request body with that property's value before the handler runs, so the handler receives a different object than the one that satisfied the schema. An authenticated low-privilege caller can use this to make nested data replace the validated body and trigger an operation the route schema did not authorize, leading to unauthorized state changes and data disclosure. Users should upgrade to fastify 5.12.2 or later.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N","score":8.1},"cwes":["CWE-20"],"references":["https://cna.openjsf.org/security-advisories.html","https://github.com/fastify/fastify/security/advisories/GHSA-667r-xxjv-c9mm"],"products":["fastify:fastify"],"source":"nvd","synced_at":"2026-10-19T22:52:03.409947763+00:00"},"epss":{"cve":"CVE-2026-84504","score":0.00428,"percentile":0.37109,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-667r-xxjv-c9mm","url":"https://osv.dev/vulnerability/GHSA-667r-xxjv-c9mm","summary":"fastify vulnerable to request body replacement via an async validation result collision","modified":"2026-10-01T00:00:04.671540564Z","packages":[{"ecosystem":"npm","name":"fastify","purl":"pkg:npm/fastify","ranges":["<5.12.2"],"fixed":["5.12.2"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}