{"cve":"CVE-2026-84428","nvd":{"published":"2026-09-04T11:17:19.317","modified":"2026-09-15T19:54:32.420","status":"Analyzed","description":"fastify versions before 5.12.2 implement the case-insensitive nature of HTTP header names by lowercasing names in a route's header schema before compiling it, but the transformation is incomplete: it lowercases the properties keys and the root-level required array, and does not lowercase the trigger and dependent names inside the JSON Schema Draft 7 dependencies keyword. Because Node stores request header names in lowercase, a canonical-case dependency such as requiring an authentication header whenever a privileged-mode header is present never matches, and the presence assertion is silently skipped. An unauthenticated remote client can therefore send the header that activates a privileged branch while omitting the header the dependency was meant to require, bypassing the conditional check. 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:N/UI:N/S:U/C:N/I:H/A:N","score":7.5},"cwes":["CWE-178"],"references":["https://cna.openjsf.org/security-advisories.html","https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58"],"products":["fastify:fastify"],"source":"nvd","synced_at":"2026-10-19T22:52:03.409947763+00:00"},"epss":{"cve":"CVE-2026-84428","score":0.00524,"percentile":0.44487,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-9q9j-q6p8-xq58","url":"https://osv.dev/vulnerability/GHSA-9q9j-q6p8-xq58","summary":"fastify vulnerable to header validation bypass via incomplete schema case normalization","modified":"2026-10-01T00:00:05.759936763Z","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."]}