long long UnserializeUInt(IMkvReader* pReader, long long pos, long long size) {
 if (!pReader || pos < 0 || (size <= 0) || (size > 8))
 return E_FILE_FORMAT_INVALID;

 long long result = 0;

 for (long long i = 0; i < size; ++i) {
 unsigned char b;

 const long status = pReader->Read(pos, 1, &b);

 if (status < 0)
 return status;

    result <<= 8;
    result |= b;

 ++pos;
 }

 return result;
}

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.