How to Fix HTTP Error 500.21 and 403.14 in ASP.NET Core on IIS

How to Fix HTTP Error 500.21 and 403.14 in ASP.NET Core on IIS

Deploying an ASP.NET Core application on IIS can sometimes lead to confusing errors like 500.21 (Bad Module) or 403.14 (Directory Listing Denied). These errors are usually not caused by your application code, but by server configuration issues.

This guide walks through the exact causes and step-by-step solutions based on a real troubleshooting flow.

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🔴 Common Errors You May See

1. HTTP Error 500.21 – Internal Server Error

Message:

Handler "aspNetCore" has a bad module "AspNetCoreModuleV2"

2. HTTP Error 403.14 – Forbidden

Message:

The Web server is configured to not list the contents of this directory

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🧠 Understanding the Problem

ASP.NET Core apps do not run directly inside IIS like classic ASP.NET apps. Instead:

• IIS uses a module called AspNetCoreModuleV2

• This module forwards requests to your application (.dll)

If this module is missing or misconfigured, IIS cannot run your app.

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✅ Step-by-Step Fix

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✅ Step 1: Install .NET Hosting Bundle

This is the most important step.

Why?

The hosting bundle installs:

• ASP.NET Core Runtime

• IIS Integration Module (AspNetCoreModuleV2)

Fix:

1. Download the correct version of the .NET Hosting Bundle

2. Install it as Administrator

⚠️ Installing only SDK or Runtime is NOT enough

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✅ Step 2: Restart IIS

After installation:

iisreset

This ensures IIS loads the new module.

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✅ Step 3: Verify Module Installation

Check if the module exists:

Option A: File check

C:\Program Files\IIS\Asp.Net Core Module\V2\aspnetcorev2.dll

Option B: IIS Manager

• Open IIS Manager

• Go to Server → Modules

• Look for:

  AspNetCoreModuleV2

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❌ If Module Exists but Not Showing

This means the module is not registered.

Fix (Manual Registration):

Run Command Prompt as Administrator:

cd %windir%\system32\inetsrv
appcmd install module /name:AspNetCoreModuleV2 /image:"C:\Program Files\IIS\Asp.Net Core Module\V2\aspnetcorev2.dll"

Then:

iisreset

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✅ Step 4: Restore Correct web.config

Your web.config must include the handler:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <location path="." inheritInChildApplications="false">
    <system.webServer>

      <handlers>
        <add name="aspNetCore"
             path="*"
             verb="*"
             modules="AspNetCoreModuleV2"
             resourceType="Unspecified" />
      </handlers>

      <aspNetCore processPath="dotnet"
                  arguments="Hajri.dll"
                  stdoutLogEnabled="true"
                  stdoutLogFile=".\logs\stdout"
                  hostingModel="inprocess" />

    </system.webServer>
  </location>
</configuration>

❌ Removing this handler will break your app

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❌ Step 5: Fix 403.14 Error

If you see:

Directory Listing Denied

Cause:

IIS is treating your app like a static folder.

Fix:

Make sure you deployed the publish output, not source code.

Correct folder should contain:

Hajri.dll
Hajri.runtimeconfig.json
Hajri.deps.json
web.config
wwwroot/

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✅ Step 6: Publish Correctly

Run:

dotnet publish -c Release -o publish

Upload contents of /publish folder to your IIS site directory.

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⚠️ Common Mistakes to Avoid

• ❌ Installing only .NET SDK

• ❌ Removing AspNetCoreModuleV2 handler

• ❌ Uploading project files instead of publish output

• ❌ Not restarting IIS after installation

• ❌ Installing hosting bundle before IIS

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🔍 Debugging Tips

Enable logs temporarily:

stdoutLogEnabled="true"

Create /logs folder and give write permission.

Then check:

/logs/stdout_*.log

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🧠 Summary

Problem	Cause	Fix
500.21	Module missing	Install Hosting Bundle
Module not visible	Not registered	Use appcmd install module
403.14	App not detected	Deploy publish folder
Static file handler	Handler removed	Restore web.config

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🚀 Final Result

Once everything is configured correctly:

• IIS loads AspNetCoreModuleV2

• Requests are forwarded to your app

• Your ASP.NET Core application runs successfully

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🎯 Key Takeaway

If IIS doesn’t recognize AspNetCoreModuleV2, your app will never run — no matter how correct your code is.

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This issue is purely environment + IIS configuration, not an application bug.

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