How to Block Invalid Image File Threats using Node.js

Cybersecurity researchers regularly identify vulnerabilities in the image rendering/processing libraries and applications that we use in and alongside our web applications. If we aren’t careful, sophisticated threat actors can exploit these vulnerabilities with specially crafted malicious image files, and these exploits can lead to devastating cyberattacks attacks (e.g., denial-of-service & remote code execution) that exfiltrate sensitive data from our system and/or permanently damage our brand reputation.

To prevent such attacks, it’s important that we 1) regularly update our software and 2) implement security policies that ensure image files rigorously conform to formatting standards before they reach a potentially vulnerable technology.

Using the below code, we can take advantage of a free security API that incorporates powerful, customizable content validation parameters along with virus and malware scanning capabilities. We can use this API to identify invalid images (i.e., those with contents that do not conform to format standards), and we can also use this API to whitelist acceptable image formats & avoid unwanted file types altogether.

To call this API, we can start by installing the SDK. We can either run the following command:

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

Or we can add the following snippet to our package.json instead:

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

With installation out of the way, we can now change gears and acquire a free API key to authorize our eventual API requests. With a free-tier API key, we can make up to 800 API calls per month with no additional commitments. Once we hit our limit, our total will reset the following month.

When we’re ready, we can copy the ready-to-run code examples below into our file to make our API calls.

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);

We can set the allowInvalidFiles parameter to “false” and block any image files that fail to pass an in-depth content validation check against their format standards. Additionally (or alternatively), we can set the restrictFileTypes parameter by entering a comma-separated list of acceptable image format extensions. If we entered the list ‘.png,.jpg,.webp’, for example, all image files would be validated against those three formatting standards, and any formats beyond that list would fail a validation check — regardless of their actual validity.

The underlying service supports 100+ image formats, PDF formats, Office formats, and more. We can also set parameters against executables, scripts, password-protected files, macros, and other threating file types.