FPDF_BOOL PDFiumEngine::Form_PostRequestURL(FPDF_FORMFILLINFO* param,
                                            FPDF_WIDESTRING url,
                                            FPDF_WIDESTRING data,
                                            FPDF_WIDESTRING content_type,
                                            FPDF_WIDESTRING encode,
                                            FPDF_WIDESTRING header,
                                            FPDF_BSTR* response) {
  std::string url_str =
      base::UTF16ToUTF8(reinterpret_cast<const base::char16*>(url));
  std::string data_str =
      base::UTF16ToUTF8(reinterpret_cast<const base::char16*>(data));
  std::string content_type_str =
      base::UTF16ToUTF8(reinterpret_cast<const base::char16*>(content_type));
  std::string encode_str =
      base::UTF16ToUTF8(reinterpret_cast<const base::char16*>(encode));
  std::string header_str =
      base::UTF16ToUTF8(reinterpret_cast<const base::char16*>(header));

  std::string javascript = "alert(\"Post:"
      + url_str + "," + data_str + "," + content_type_str + ","
      + encode_str + "," + header_str
      + "\")";
  return true;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.