CVE-2026-84428
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, …
Impact
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 packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| npm | fastify | < 5.12.2 | 5.12.2 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Fastify | Fastify | before 5.12.2 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-9q9j-q6p8-xq58
- https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58
- https://nvd.nist.gov/vuln/detail/CVE-2026-84428
- https://github.com/fastify/fastify/commit/179619c8e99d54924309b9933402151ef9af37e0
- https://cna.openjsf.org/security-advisories.html
- https://github.com/fastify/fastify/releases/tag/v5.12.2