How to Block .EXE File Uploads using C#/.NET Core

Cloudmersive
4 min readMay 26, 2023

While most .EXE files we encounter are needed to run legitimate software applications, the executable file format also provides an ideal means for threat actors to inject malicious code into our system. As a result, it’s important to be extremely cautious about clicking on .EXE files from untrustworthy sources — and it’s best to block them entirely from reaching our data storage layers.

The Advanced Virus Scan API provided in this article is free-to-use and allows you to easily block .EXE files by setting a simple request parameter (allowExecutables) to “False”. As the API name suggests, this service will also perform an in-depth virus and malware scan for your files, returning a CleanResult: False value when files are found to be infected. This same response is returned for any file violating your custom anti-executable policy, making it easy to block multiple attack vectors in one request.

To take advantage of this API using C#/.NET Core, first run the following command in the Package Manager console to install the SDK via NuGet:

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

After that, copy and paste from the ready-to-run code examples below to structure your API call:

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 authenticate your request with a free-tier API key and scan up to 800 files per month (with no commitments upon reaching that limit). That’s all there is to it!

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