The product initializes or sets a resource with a default that is intended to be changed by the product's installer, administrator, or maintainer, but the default is not secure.
The impact of insecure defaults varies widely depending on the functionality that the product controls.
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)