Unauthenticated file write via unchecked upload path

Path traversal in kekingcn kkFileView 5.0.0 through 5.0.2 allows remote attackers to write files outside fileDir via upload requests. The fileUpload and createFolder handlers append the unvalidated path parameter to the demo upload root; existsFile checks the same escaped path before fileUpload writes bytes. Exploitation requires an exposed service with file uploads enabled, which upstream configuration disables by default; writes remain limited by server filesystem permissions and allowed filename extensions.