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7.5 High

CVE-2026-84469 fastify versions before 5.12.2 decide whether to compile a request schema based on JavaScript truthiness, but JSON…

Description

fastify versions before 5.12.2 decide whether to compile a request schema based on JavaScript truthiness, but JSON Schema Draft 7 defines the boolean false as a valid schema that rejects every instance. When an application assigns false to a route's body, querystring, params, or headers schema to deny all input, fastify treats it as a missing schema, compiles no validator, and runs the route handler on any request. An unauthenticated remote client can therefore reach a handler that a valid deny-all schema was intended to make unreachable, a complete validation bypass that can lead to unauthorized state changes or execution of disabled operations. Users should upgrade to fastify 5.12.2 or later.

Affected products and versions

Product Affected versions Fixed in
fastify 5.12 earliest → < 5.12.2 5.12.2

References

Timeline

  1. Published
  2. Last modified

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