Fastify up to 5.12.5 Header Validation input validation

Summaryinfo

A vulnerability categorized as problematic has been discovered in Fastify up to 5.12.5. Impacted is an unknown function of the component Header Validation. The manipulation results in input validation. This vulnerability is reported as CVE-2026-107832. The attack can be launched remotely. No exploit exists. It is advisable to upgrade the affected component.

Detailsinfo

A vulnerability was found in Fastify up to 5.12.5. It has been classified as problematic. Affected is an unknown functionality of the component Header Validation. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on integrity. CVE summarizes:

fastify is a fast and low overhead web framework for Node.js. In versions 5.12.2 through 5.12.5, the routine that lowercases header names declared in a route schema does not lowercase the enum or const header names nested inside a propertyNames subschema. As a result, a header allow-list or deny-list written with canonical (non-lowercase) casing never matches the incoming lowercased header, so a restricted header passes validation and reaches the route handler. An attacker can therefore bypass a case-sensitive header validation rule and smuggle a forbidden header past the schema, affecting the integrity of request handling. The issue is fixed in fastify 5.12.6, and users should upgrade to 5.12.6 or later. There is no workaround other than upgrading, though applications can declare header names in lowercase to avoid the mismatch.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-107832 since 10/08/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. The technical details are unknown and an exploit is not available.

Upgrading to version 5.12.6 eliminates this vulnerability.

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Productinfo

Name

• Fastify

Version

• 5.12.0
• 5.12.1
• 5.12.2
• 5.12.3
• 5.12.4
• 5.12.5

Website

• Product: https://github.com/fastify/fastify/

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