The system must only accept files whose format (structure) is required by the business operation.
CWE-646: Reliance on File Name or Extension of Externally-Supplied File. The software allows a file to be uploaded, but it relies on the file name or extension of the file to determine the appropriate behaviors. This could be used by attackers to cause the file to be misclassified and processed in a dangerous fashion.
OWASP-ASVS v4.0.1 V12.2 File Integrity Requirements.(12.2.1) Verify that files obtained from untrusted sources are validated to be of expected type based on the file’s content.