Blazor Wasm Antivirus Protection

⚠️⚠️ NOT RECOMMENDED FOR .NET 8.0+ ⚠️⚠️: Please use the new Webcil format that is enabled by default in .NET 8.0. More info here.

This package attempts to guard against false positives from antiviruses that flag Blazor Wasm as malware (up to .NET version 7.0).

Confirmed success against:

1. BitDefender Total Security (v26.0.10.45)
2. BitDefender Endpoint Security Tool (v7.4.3.146)
3. Smoothwall Firewall - Confirmed by peterthorpe81
4. Sophos Endpoint Agent - Confirmed by peterthorpe81
5. Forcepoint Firewall - Confirmed by egil
6. GDATA Internet Security - Confirmed by paulguz-datapa

📣 If you have used this package and has helped you bypass any false positives from other security software, please consider creating an issue with your experience to contribute to this list.

🛡️ You can use virustotal's online scanner for some indication of how various antiviruses view your site.

What does this package do ?

This package injects some custom MSBuild tasks that do the following during publishing:

1. Obfuscates all client assemblies so that firewalls and antiviruses don't see them as executables. Obfuscation methods supported:
   • Using a key to XOR all client assemblies (default) .
   • OR
   • Changing the MZ header of all client assemblies to BZ, a custom header (less aggressive - more info here) .
2. Renames the extension of all client assemblies from .dll to .bin .
3. Swaps Blazor's default caching mechanism with a custom one that saves the obfuscated assemblies to the cache instead of the unobfuscated ones. This is because some antiviruses are flaging the cached Blazor files that are being saved on the disk by the browser.
4. Adds a beforeStart Blazor initialization method (more info here), that uses a custom loadBootResource function to restore the obfuscation of the assemblies after downloaded, but before loaded by dotnet.wasm.

How to use

1. Add the nuget package in your Client (wasm) AND your Server (if using Blazor wasm hosted) projects.

dotnet add package BlazorWasmAntivirusProtection

2. (Progressive Web Applications only): If you are using the Blazor Wasm PWA template, update the following line in your service-worker.published.js file to include .bin files:

const offlineAssetsInclude = [/\.bin$/, /\.dll$/, /\.pdb$/, /\.wasm/, /\.html/, /\.js$/, /\.json$/, /\.css$/, /\.woff$/, /\.png$/, /\.jpe?g$/, /\.gif$/, /\.ico$/, /\.blat$/, /\.dat$/ ];

3. Publish your app in Release mode and test it!

dotnet publish Server\BlazorHostedSampleApp.Server.csproj -c Release

Nuget package page can be found here.

Considerations

While using XOR obfuscation does not change the actual size of a dll file, it does affect its compressed size. The bigger the XOR key used, the worse the compression gets.

The default XOR key is the string bwap.

Known Issues

Disabling trimming in your project and using this package at the same time is not supported. There is an issue tracking this limitation here.

<!-- Not Supported -->
<PublishTrimmed>false</PublishTrimmed>

Configuration

The following options allow you to customize the tasks executed by this package.

Custom dll rename extension

If you want to use a different extension for renaming dlls, for example ".blz", add the following property in the published project's .csproj file (Server project if using Blazor hosted).

<RenameDllsTo>blz</RenameDllsTo>

Disable dll rename

You can disable dll renaming by adding the following property in the published project's .csproj file (Server project if using Blazor hosted).

<DisableRenamingDlls>true</DisableRenamingDlls>

Changing or disabling dll obfuscation

You can change or disable dll obfuscation by adding the following property in your Client project's .csproj file. Supported values:

• None
• ChangeHeaders
• Xor (default)

<!-- Disables dll obfuscation -->
<ObfuscationMode>None</ObfuscationMode> 

Changing the XOR obfuscation key

You can change the key that is used for the XOR obfuscation adding the following property in your Client project's .csproj file.

<!-- Changes the dll obfuscation xor key -->
<XorKey>mykey</XorKey>

Disable caching

You can disable boot resources caching by using the following property in your Client project's .csproj file, just as you would in any Blazor project. More info here.

<BlazorCacheBootResources>false</BlazorCacheBootResources>

Special Thanks

This work was inspired by the post in https://github.com/dotnet/aspnetcore/issues/31048#issuecomment-915152791 by github user tedd

Release Notes