Bug 2550519 (CVE-2026-107832)

Summary: CVE-2026-107832 fastify: fastify: Header validation bypass via incomplete schema case normalization
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
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Priority: low    
Version: unspecifiedCC: bbrownin, sdawley
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in fastify. The framework's route schema validation fails to properly normalize the casing of header names declared within nested property name schemas. A remote attacker can exploit this vulnerability by submitting requests with restricted headers, bypassing header allow-lists or deny-lists configured with canonical casing. Consequently, forbidden headers can reach route handlers and undermine the integrity of request processing.
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Description OSIDB Bzimport 2026-10-13 13:53:01 UTC 
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.