Impact
fastify before 5.12.1, when a route uses a root-level primitive body schema (for example an integer with a minimum and maximum) and the default type coercion, validates the coerced value but exposes the original, uncoerced value to the route handler. For example, a JSON body "10" is coerced to the number 10 and passes an integer 1 to 10 schema, but request.body stays the string "10". An application that trusts the validated type is handed a value that did not satisfy the schema, which can bypass limits the application enforces on that typed value. Object and array body schemas are not affected, they coerce their members in place.
Patches
Upgrade to fastify 5.12.1.
Workarounds
Until you can upgrade, avoid relying on the validated type of a root primitive body. Wrap the value in an object schema (object properties are coerced in place), for example accept { "value": 10 } and read request.body.value, or re-check the type in the handler.
References
velgusgus599 Reporter
mcollina Remediation developer
UlisesGascon Remediation reviewer
Impact
fastifybefore 5.12.1, when a route uses a root-level primitive body schema (for example an integer with a minimum and maximum) and the default type coercion, validates the coerced value but exposes the original, uncoerced value to the route handler. For example, a JSON body"10"is coerced to the number10and passes an integer 1 to 10 schema, butrequest.bodystays the string"10". An application that trusts the validated type is handed a value that did not satisfy the schema, which can bypass limits the application enforces on that typed value. Object and array body schemas are not affected, they coerce their members in place.Patches
Upgrade to
fastify5.12.1.Workarounds
Until you can upgrade, avoid relying on the validated type of a root primitive body. Wrap the value in an object schema (object properties are coerced in place), for example accept
{ "value": 10 }and readrequest.body.value, or re-check the type in the handler.References