{"id":"CVE-2026-107832","aliases":["GHSA-389g-gv7q-r4x8"],"url":"https://o3.security/vulnerability/CVE-2026-107832","summary":"fastify 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.","published":"2026-10-13T13:23:24.217Z","modified":"2026-10-21T02:52:27.363360121Z","cvss":{"score":3.7,"severity":"LOW","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"fastify","fixedVersion":"5.12.6"}],"fix":{"url":"https://github.com/fastify/fastify/pull/7104","label":"fastify/fastify#7104"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/107xxx/CVE-2026-107832.json"},{"type":"ADVISORY","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":"PACKAGE","url":"https://github.com/fastify/fastify"},{"type":"WEB","url":"https://github.com/fastify/fastify/releases/tag/v5.12.6"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T02:52:27.363360121Z"}}