# CVE-2026-84428

## Summary

- **CVE ID:** CVE-2026-84428
- **Severity:** HIGH
- **CVSS Score:** 7.5 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N)
- **CWE:** CWE-178
- **Published:** Sep 4, 2026
- **Last Modified:** Sep 4, 2026

## 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.

## Affected Products

- fastify — fastify (0)
- fastify — fastify (5.12.2)

## References

- [CNA](https://github.com/fastify/fastify/security/advisories/GHSA-9q9j-q6p8-xq58)
- [CNA](https://cna.openjsf.org/security-advisories.html)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.28%
- **EPSS Percentile:** 20.6

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._