 static MagickBooleanType ConcatenateImages(int argc,char **argv,
     ExceptionInfo *exception )
 {
   FILE
     *input,
     *output;
 
   int
     c;
 
  register ssize_t
    i;
 
   if (ExpandFilenames(&argc,&argv) == MagickFalse)
     ThrowFileException(exception,ResourceLimitError,"MemoryAllocationFailed",
         GetExceptionMessage(errno));
   output=fopen_utf8(argv[argc-1],"wb");
  if (output == (FILE *) NULL) {
    ThrowFileException(exception,FileOpenError,"UnableToOpenFile",argv[argc-1]);
    return(MagickFalse);
  }
  for (i=2; i < (ssize_t) (argc-1); i++) {
#if 0
    fprintf(stderr, "DEBUG: Concatenate Image: \"%s\"\n", argv[i]);
#endif
     input=fopen_utf8(argv[i],"rb");
    if (input == (FILE *) NULL) {
         ThrowFileException(exception,FileOpenError,"UnableToOpenFile",argv[i]);
         continue;
       }
     for (c=fgetc(input); c != EOF; c=fgetc(input))
      (void) fputc((char) c,output);
     (void) fclose(input);
     (void) remove_utf8(argv[i]);
   }
   (void) fclose(output);
  return(MagickTrue);
 }

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.