The product uses or accesses a file descriptor after it has been closed.
After a file descriptor for a particular file or device has been released, it can be reused. The code might not write to the original file, since the reused file descriptor might reference a different file or device.
The program could read data from the wrong file.
Accessing a file descriptor that has been closed can cause a crash.
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.)