{"id":"GHSA-389g-gv7q-r4x8","summary":"fastify is vulnerable to header validation bypass via case-sensitive propertyNames","details":"### Impact\n\nFastify lowercases header names in a `headers` schema before compilation, because Node.js stores request header names in lowercase. This normalization does not reach the header names held in a `propertyNames` subschema's `enum` and `const`. A header-name deny-list written in the canonical header case, such as `propertyNames: { not: { enum: ['X-Debug-Override'] } }`, therefore never matches the lowercased request headers, and the forbidden header reaches the handler. Any application that uses a `propertyNames` deny-list or allow-list to constrain request header names does not get the constraint it expects. The same rule written in lowercase works, and the `not: { required: [...] }` form is unaffected, so this is a gap in the built-in normalization rather than a wrong schema. This is an incomplete fix of CVE-2026-84428 ([GHSA-9q9j-q6p8-xq58](https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58)), whose normalization covered header names used as property keys but not those used as values inside `propertyNames`.\n\n### Patches\n\nUsers should upgrade to fastify `5.12.6` or later, which lowercases header names held in `enum` and `const` inside a `propertyNames` subschema so they match the lowercased request headers. Header-name constraints that cannot be normalized automatically, regular expressions (`propertyNames` `pattern` and `patternProperties` keys) and a `$ref` used inside `propertyNames`, are documented and, for the `$ref` case, warned at startup (`FSTSEC003`). Author those to match the lowercased request headers.\n\n### Workarounds\n\nWrite the `propertyNames` header-name constraint in lowercase (for example `enum: ['x-debug-override']`), or enforce the header check in an `onRequest` or `preValidation` hook instead of the schema.","aliases":["CVE-2026-107832"],"modified":"2026-10-22T16:45:04.287484964Z","published":"2026-10-22T16:40:35Z","database_specific":{"cwe_ids":["CWE-178"],"severity":"LOW","github_reviewed":true,"github_reviewed_at":"2026-10-22T16:40:35Z","nvd_published_at":"2026-10-13T14:17:19Z"},"references":[{"type":"WEB","url":"https://github.com/fastify/fastify/security/advisories/GHSA-389g-gv7q-r4x8"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-107832"},{"type":"WEB","url":"https://github.com/fastify/fastify/pull/7104"},{"type":"WEB","url":"https://github.com/fastify/fastify/commit/3241fbd2f10a8ca1503533726836b53b6e8775a2"},{"type":"WEB","url":"https://github.com/fastify/fastify/commit/35c32375731c111439682b2f9e6e0baed2694269"},{"type":"WEB","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"PACKAGE","url":"https://github.com/fastify/fastify"},{"type":"WEB","url":"https://github.com/fastify/fastify/releases/tag/v5.12.6"}],"affected":[{"package":{"name":"fastify","ecosystem":"npm","purl":"pkg:npm/fastify"},"ranges":[{"type":"SEMVER","events":[{"introduced":"5.12.2"},{"fixed":"5.12.6"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-389g-gv7q-r4x8/GHSA-389g-gv7q-r4x8.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"}]}