CVE-2026-107832

/// Technical description

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.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References