How to Remove Password Protected File Uploads using C#/.NET Core

Password protected files are a tried & true cyber-attack vector, allowing threat actors to inject malicious code into a system by hiding it behind the security and encryption features built into many common file formats. Since attacks using password protected files are typically carried out with social engineering tactics (i.e., convincing the victim to use an externally supplied password to unlock the file), part of mitigating this form of threat boils down to our own discretion. It’s generally best, however, to disallow external password protected files from entering our system entirely.

We can easily block password protected file uploads to any application in our system using the free Virus Scanning API provided below. This API will check files for millions of potential virus and malware signatures, and password protected files can be blocked by setting the allowPasswordProtectedFiles Boolean to “False” in the API request body. Any files breaching this API’s built in & custom security policies will receive a CleanResult: False value in the API response, making it easy to quickly delete or quarantine any potentially infected documents.

To quickly take advantage of this API using ready-to-run C# code examples, let’s start by running the following command to install the .NET Core SDK:

Install-Package Cloudmersive.APIClient.NETCore.VirusScan -Version 2.0.4

After that, let’s structure our API call using the following code:

using System;
using System.Diagnostics;
using Cloudmersive.APIClient.NETCore.VirusScan.Api;
using Cloudmersive.APIClient.NETCore.VirusScan.Client;
using Cloudmersive.APIClient.NETCore.VirusScan.Model;

namespace Example
{
    public class ScanFileAdvancedExample
    {
        public void main()
        {
            // Configure API key authorization: Apikey
            Configuration.Default.AddApiKey("Apikey", "YOUR_API_KEY");

            var apiInstance = new ScanApi();
            var inputFile = new System.IO.FileStream("C:\\temp\\inputfile", System.IO.FileMode.Open); // System.IO.Stream | Input file to perform the operation on.
            var allowExecutables = true;  // bool? | Set to false to block executable files (program code) from being allowed in the input file.  Default is false (recommended). (optional) 
            var allowInvalidFiles = true;  // bool? | 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). (optional) 
            var allowScripts = true;  // bool? | 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). (optional) 
            var allowPasswordProtectedFiles = true;  // bool? | 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). (optional) 
            var allowMacros = true;  // bool? | 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). (optional) 
            var allowXmlExternalEntities = true;  // bool? | 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). (optional) 
            var allowInsecureDeserialization = true;  // bool? | 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). (optional) 
            var allowHtml = true;  // bool? | 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]. (optional) 
            var 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. (optional) 

            try
            {
                // Advanced Scan a file for viruses
                VirusScanAdvancedResult result = apiInstance.ScanFileAdvanced(inputFile, allowExecutables, allowInvalidFiles, allowScripts, allowPasswordProtectedFiles, allowMacros, allowXmlExternalEntities, allowInsecureDeserialization, allowHtml, restrictFileTypes);
                Debug.WriteLine(result);
            }
            catch (Exception e)
            {
                Debug.Print("Exception when calling ScanApi.ScanFileAdvanced: " + e.Message );
            }
        }
    }
}

Now you can easily block password protected files and a variety of other virus, malware and non-malware threats in a single request.

To authenticate your requests for free, supply a free-tier API key; this can be obtained by registering a free account on the Cloudmersive website.