This library allows you to add Content Security Policy, Strict Transport Security and Public Key Pin headers via middleware.
You can get the library from NuGet: https://www.nuget.org/packages/Joonasw.AspNetCore.SecurityHeaders
// Enable Strict Transport Security with a 30-day caching period
// Do not include subdomains
// Do not allow preload
app.UseStrictTransportSecurity(new HstsOptions(TimeSpan.FromDays(30), includeSubDomains: false, preload: false));
// Use certificate pinning with:
// - 30-day caching period
// - One pin in SHA-256 form
// - Report-Only = Invalid certificate should not be reported, but:
// - Report problems to /hpkp-report
app.UseHpkp(hpkp =>
{
hpkp.UseMaxAgeSeconds(30 * 24 * 60 * 60)
.AddSha256Pin("nrmpk4ZI3wbRBmUZIT5aKAgP0LlKHRgfA2Snjzeg9iY=")
.SetReportOnly()
.ReportViolationsTo("/hpkp-report");
});
// Content Security Policy
app.UseCsp(csp =>
{
// If nothing is mentioned for a resource class, allow from this domain
csp.ByDefaultAllow
.FromSelf();
// Allow JavaScript from:
csp.AllowScripts
.FromSelf() //This domain
.From("localhost:1591") //These two domains
.From("ajax.aspnetcdn.com");
// CSS allowed from:
csp.AllowStyles
.FromSelf()
.From("ajax.aspnetcdn.com");
csp.AllowImages
.FromSelf();
// HTML5 audio and video elemented sources can be from:
csp.AllowAudioAndVideo
.FromNowhere();
// Contained iframes can be sourced from:
csp.AllowFrames
.FromNowhere(); //Nowhere, no iframes allowed
// Allow AJAX, WebSocket and EventSource connections to:
csp.AllowConnections
.To("ws://localhost:1591")
.To("http://localhost:1591")
.ToSelf();
// Allow fonts to be downloaded from:
csp.AllowFonts
.FromSelf()
.From("ajax.aspnetcdn.com");
// Allow object, embed, and applet sources from:
csp.AllowPlugins
.FromNowhere();
// Allow other sites to put this in an iframe?
csp.AllowFraming
.FromNowhere(); // Block framing on other sites, equivalent to X-Frame-Options: DENY
// Do not block violations, only report
// This is a good idea while testing your CSP
// Remove it when you know everything will work
csp.SetReportOnly();
// Where should the violation reports be sent to?
csp.ReportViolationsTo("/csp-report");
// Do not include the CSP header for requests to the /api endpoints
csp.OnSendingHeader = context =>
{
context.ShouldNotSend = context.HttpContext.Request.Path.StartsWithSegments("/api");
return Task.CompletedTask;
};
});
Content Security Policy can be quite daunting. Here is a nice page to find out what the options do: https://content-security-policy.com/
For violation reports, I recommend using Scott Helme's Report URI service at https://report-uri.io/.
CSP allows you to also specify a nonce value, which makes it easier to have inline script and style elements like this on a page:
<head>
<script>
console.log("Hello");
</script>
<style>
h1 {
color: red;
}
</style>
</head>
To allow them without nonces, you might have to use the unsafe-inline option.
Instead of doing that, we can add the following service in Startup:
public void ConfigureServices(IServiceCollection services)
{
// ... other service registrations
// Add services necessary for nonces in CSP, 32-byte nonces
services.AddCsp(nonceByteAmount: 32);
}
Then you need to modify your CSP definition to include the nonce:
csp.AllowScripts
.FromSelf()
.From("localhost:1591")
.From("ajax.aspnetcdn.com")
.AddNonce(); //<----
csp.AllowStyles
.FromSelf()
.From("ajax.aspnetcdn.com")
.AddNonce(); //<-----
Then to use the nonce tag helper, we need to import it in _ViewImports.cshtml:
@addTagHelper *, Joonasw.AspNetCore.SecurityHeaders
Then we just need to use it in the Razor view:
<head>
<script asp-add-nonce="true">
console.log("Hello");
</script>
<style asp-add-nonce="true">
h1 {
color: red;
}
</style>
</head>
Now a unique nonce is generated every request and inserted into the CSP header + the elements you want.
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