How to Check XLTX Files for OLE in Node.js

Just like regular XLSX files, Excel template files — XLTX — support object linking & embedding (OLE). Depending on where an XLTX file came from, OLE can indicate a potential risk.

While OLE is intended to seamlessly connect content from different applications in our Office ecosystem, it can, unfortunately, also be exploited to booby-trap Office files with malicious links and objects.

Thankfully, using a free API, we can check if XLTX file uploads have OLE enabled. This API will also scan our file for virus and malware signatures, and it’ll detect a wide range of additional threats (e.g., identify if the file is invalid or masquerading as another file type).

We can structure our API call in a few quick steps. To install the SDK via NPM install, let’s run the following command:

npm install cloudmersive-virus-api-client --save

Alternatively, we can add this snippet to our package.json:

  "dependencies": {
    "cloudmersive-virus-api-client": "^1.1.9"
  }

Now let’s focus quickly on API call authorization. We’ll need a free Cloudmersive API key to authorize our requests (this will allow a limit of 800 API calls per month with no commitments).

With our API key ready, we can now call the function using the below code examples:

var CloudmersiveVirusApiClient = require('cloudmersive-virus-api-client');
var defaultClient = CloudmersiveVirusApiClient.ApiClient.instance;

// Configure API key authorization: Apikey
var Apikey = defaultClient.authentications['Apikey'];
Apikey.apiKey = 'YOUR API KEY';



var apiInstance = new CloudmersiveVirusApiClient.ScanApi();

var inputFile = Buffer.from(fs.readFileSync("C:\\temp\\inputfile").buffer); // File | Input file to perform the operation on.

var opts = { 
  'allowExecutables': true, // Boolean | Set to false to block executable files (program code) from being allowed in the input file.  Default is false (recommended).
  'allowInvalidFiles': true, // Boolean | Set to false to block invalid files, such as a PDF file that is not really a valid PDF file, or a Word Document that is not a valid Word Document.  Default is false (recommended).
  'allowScripts': true, // Boolean | Set to false to block script files, such as a PHP files, Python scripts, and other malicious content or security threats that can be embedded in the file.  Set to true to allow these file types.  Default is false (recommended).
  'allowPasswordProtectedFiles': true, // Boolean | Set to false to block password protected and encrypted files, such as encrypted zip and rar files, and other files that seek to circumvent scanning through passwords.  Set to true to allow these file types.  Default is false (recommended).
  'allowMacros': true, // Boolean | Set to false to block macros and other threats embedded in document files, such as Word, Excel and PowerPoint embedded Macros, and other files that contain embedded content threats.  Set to true to allow these file types.  Default is false (recommended).
  'allowXmlExternalEntities': true, // Boolean | Set to false to block XML External Entities and other threats embedded in XML files, and other files that contain embedded content threats.  Set to true to allow these file types.  Default is false (recommended).
  'allowInsecureDeserialization': true, // Boolean | Set to false to block Insecure Deserialization and other threats embedded in JSON and other object serialization files, and other files that contain embedded content threats.  Set to true to allow these file types.  Default is false (recommended).
  'allowHtml': true, // Boolean | Set to false to block HTML input in the top level file; HTML can contain XSS, scripts, local file accesses and other threats.  Set to true to allow these file types.  Default is false (recommended) [for API keys created prior to the release of this feature default is true for backward compatability].
  'restrictFileTypes': "restrictFileTypes_example" // String | Specify a restricted set of file formats to allow as clean as a comma-separated list of file formats, such as .pdf,.docx,.png would allow only PDF, PNG and Word document files.  All files must pass content verification against this list of file formats, if they do not, then the result will be returned as CleanResult=false.  Set restrictFileTypes parameter to null or empty string to disable; default is disabled.
};

var callback = function(error, data, response) {
  if (error) {
    console.error(error);
  } else {
    console.log('API called successfully. Returned data: ' + data);
  }
};
apiInstance.scanFileAdvanced(inputFile, opts, callback);

Our response object will identify if OLE content was detected, and we can use that response to take subsequent actions on the file.

Now we can ensure XLTX files are OLE and malware free before we eventually share or open them.