> For the complete documentation index, see [llms.txt](https://docs.umbraco.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.umbraco.com/umbraco-cms/13.latest/extending/health-check/guides/contentsniffingprotection.md).

# Content/MIME Sniffing Protection

Protect your Umbraco site from MIME sniffing vulnerabilities using security headers like X-Content-Type-Options.

*Checks that your site contains a header used to protect against Multipurpose Internet Mail Extensions (MIME) sniffing vulnerabilities.*

## How to fix this health check

This health check can be fixed by adding a header before the response is started.

Preferable you use a security library like [NWebSec](https://docs.nwebsec.com/).

### Adding Content/MIME Sniffing Protection using NWebSec

If you take a NuGet dependency on [NWebsec.AspNetCore.Middleware/](https://www.nuget.org/packages/NWebsec.AspNetCore.Middleware/), you can use third extension methods on `WebApplication`.

```csharp
...
WebApplication app = builder.Build();

app.UseXContentTypeOptions();
...
```

### Adding Content/MIME Sniffing Protection using manual middleware

If you don't like to have a dependency on third party libraries. You can add the following custom middleware to the request pipeline.

First create the middleware class:

```csharp
namespace MySite.Middleware;

public class NoSniffMiddleware : IMiddleware
{
    public async Task InvokeAsync(HttpContext context, RequestDelegate next)
    {
        context.Response.Headers.Append("X-Content-Type-Options", "nosniff");
        await next(context);
    }
}
```

Next register it in `Program.cs`

```csharp
using MySite.Middleware;

WebApplicationBuilder builder = WebApplication.CreateBuilder(args);

builder.Services.AddSingleton<NoSniffMiddleware>();

builder.CreateUmbracoBuilder()
    .AddBackOffice()
    .AddWebsite()
    .AddDeliveryApi()
    .AddComposers()
    .Build();

WebApplication app = builder.Build();

app.UseMiddleware<NoSniffMiddleware>();

await app.BootUmbracoAsync();
...
```


---

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