How to Scan Files for Unsafe Archives using C#/.NET Core

Cloudmersive
4 min readMay 31, 2023

We can define an unsafe archive as any compressed file format with an extraction outcome that negatively impacts (or fully compromises) our system. Perhaps the most common example of this is a .ZIP bomb — an archive overloaded with data intended to crash our system once extracted.

It’s critically important to block these files from entering our system, and the free API provided below is designed to handle that task; setting the allowUnsafeArchives Boolean to “False” in the API request body will ensure all files with unsafe extraction outcomes receive a CleanResult: False value in the API response body. This API will also scan files for millions of virus and malware signatures — including ransomware and spyware — so you can ensure each new file entering your system is rigorously vetted before reaching a sensitive storage layer.

Using the complementary C# code below, you can take advantage of this API with zero hassle. First things first, run the following command to install the .NET Core SDK:

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

After that, copy and paste the below code to structure your request:

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 configure custom threat policies against unsafe archives and a variety of other non-malware content threats. To satisfy the security authentication parameter, provide a free-tier Cloudmersive API key (this can be obtained by registering a free account on the Cloudmersive website).

--

--

Cloudmersive

There’s an API for that. Cloudmersive is a leader in Highly Scalable Cloud APIs.