{"id":"CVE-2026-84428","state":"PUBLISHED","title":"fastify vulnerable to header validation bypass via incomplete schema case normalization","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.","publishedAt":"2026-09-04T10:24:27.809Z","updatedAt":"2026-09-04T16:06:04.123Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","source":"openjs"},"assigner":"openjs","products":["fastify fastify"],"affected":[{"vendor":"fastify","product":"fastify","packageURL":"pkg:npm/fastify","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"5.12.2","versionType":"semver"},{"version":"5.12.2","status":"unaffected","versionType":"semver"}]}],"references":["https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58","https://cna.openjsf.org/security-advisories.html"],"weaknesses":["CWE-178"],"ingestedAt":"2026-10-29T20:13:15.269Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/84xxx/CVE-2026-84428.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-84428","state":"PUBLISHED","datePublished":"2026-09-04T10:24:27.809Z","dateUpdated":"2026-09-04T16:06:04.123Z","assignerShortName":"openjs","assignerOrgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateReserved":"2026-09-01T18:21:51.906Z"},"containers":{"cna":{"title":"fastify vulnerable to header validation bypass via incomplete schema case normalization","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"fastify","product":"fastify","packageURL":"pkg:npm/fastify","defaultStatus":"unaffected","versions":[{"version":"0","status":"affected","lessThan":"5.12.2","versionType":"semver"},{"version":"5.12.2","status":"unaffected","versionType":"semver"}]}],"references":[{"url":"https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58"},{"url":"https://cna.openjsf.org/security-advisories.html"}],"metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-178","lang":"en","description":"CWE-178: Improper Handling of Case Sensitivity","type":"CWE"}]}],"providerMetadata":{"shortName":"openjs","orgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateUpdated":"2026-09-04T10:24:27.809Z"},"credits":[{"lang":"en","type":"reporter","value":"schecthellraiser606"},{"lang":"en","type":"remediation developer","value":"mcollina"},{"lang":"en","type":"remediation developer","value":"UlisesGascon"}],"x_generator":{"engine":"cve-kit 1.0.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-04T16:04:59.730612Z","id":"CVE-2026-84428","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-04T16:06:04.123Z"}}]}}}