How to Block Executable Uploads in C# .Net Framework

File upload attacks are rapidly on the rise in recent months, with ever-increasing portions of the hacker community adopting this attack vector as their go-to approach. If you don’t want to count yourself among the thousands of victims, you will need protection against zero-day threats. In particular, masked executables (usually renamed as seemingly harmless JPEGs or PDFs), can be very troublesome. Today, we will be setting up protection that can identify and block this type of attack.

First we need to install our client files using this command:

Install-Package Cloudmersive.APIClient.NET.VirusScan -Version 3.0.3

Next we go ahead with our function call for advanced file scanning. Make sure that allowExecutables is set to false.

using System;using System.Diagnostics;using Cloudmersive.APIClient.NET.VirusScan.Api;using Cloudmersive.APIClient.NET.VirusScan.Client;using Cloudmersive.APIClient.NET.VirusScan.Model;namespace Example{public class ScanFileAdvancedExample{public void main(){// Configure API key authorization: ApikeyConfiguration.Default.AddApiKey("Apikey", "YOUR_API_KEY");// Uncomment below to setup prefix (e.g. Bearer) for API key, if needed// Configuration.Default.AddApiKeyPrefix("Apikey", "Bearer");var apiInstance = new ScanApi();var inputFile = new System.IO.Stream(); // 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, Pythong 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 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 virusesVirusScanAdvancedResult result = apiInstance.ScanFileAdvanced(inputFile, allowExecutables, allowInvalidFiles, allowScripts, allowPasswordProtectedFiles, restrictFileTypes);Debug.WriteLine(result);}catch (Exception e){Debug.Print("Exception when calling ScanApi.ScanFileAdvanced: " + e.Message );}}}}

And that’s it! You are now fully protected.

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