The product does not follow or incorrectly follows the specifications as required by the implementation language, environment, framework, protocol, or platform.
When leveraging external functionality, such as an API, it is important that the caller does so in accordance with the requirements of the external functionality or else unintended behaviors may result, possibly leaving the system vulnerable to any number of exploits.
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.)