{"id":"CVE-2026-84428","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-84428","generatedAt":"2026-10-28T03:29:16.048Z","title":"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.","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.","published":"2026-09-04T11:17:19.000Z","lastModified":"2026-09-15T19:54:32.000Z","status":"Analyzed","sourceIdentifier":"ce714d77-add3-4f53-aff5-83d477b104bb","cvss":{"version":"3.1","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"},"cwe":["CWE-178"],"affected":["fastify/fastify"],"epss":{"score":0.00524,"percentile":0.44206,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.52%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://cna.openjsf.org/security-advisories.html","tags":["Third Party Advisory"],"source":"ce714d77-add3-4f53-aff5-83d477b104bb"},{"url":"https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58","tags":["Mitigation","Vendor Advisory"],"source":"ce714d77-add3-4f53-aff5-83d477b104bb"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-84428","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}