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Fix open redirect (CWE-601) in www-to-apex redirect middleware #1262

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Merged
BenjaminMichaelis merged 2 commits into from
Aug 7, 2026
Merged

Fix open redirect (CWE-601) in www-to-apex redirect middleware #1262

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ad63bca
Initial plan
Copilot Aug 7, 2026
e4a166a
Fix alert #16: use UriHelper.BuildAbsolute to prevent open redirect
Copilot Aug 7, 2026
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7 changes: 5 additions & 2 deletions EssentialCSharp.Web/Program.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@
using EssentialCSharp.Web.Tools;
using Mailjet.Client;
using Microsoft.AspNetCore.Authentication;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.AspNetCore.HttpOverrides;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Identity.UI.Services;
Expand Down Expand Up @@ -454,7 +455,9 @@ await context.HttpContext.Response.WriteAsync(
? configuredBaseUri.Host[4..]
: configuredBaseUri.Host;
string wwwHost = $"www.{apexHost}";
string redirectAuthority = new UriBuilder(configuredBaseUri) { Host = apexHost }.Uri.GetLeftPart(UriPartial.Authority);
Uri apexUri = new UriBuilder(configuredBaseUri) { Host = apexHost }.Uri;
string redirectScheme = apexUri.Scheme;
HostString redirectHost = new HostString(apexUri.Authority);

app.UseExceptionHandler(exceptionApp =>
{
Expand Down Expand Up @@ -531,7 +534,7 @@ await McpJsonRpcResponseWriter.WriteErrorAsync(
{
if (string.Equals(context.Request.Host.Host, wwwHost, StringComparison.OrdinalIgnoreCase))
{
string redirectUrl = $"{redirectAuthority}{context.Request.PathBase}{context.Request.Path}{context.Request.QueryString}";
string redirectUrl = UriHelper.BuildAbsolute(redirectScheme, redirectHost, context.Request.PathBase, context.Request.Path, context.Request.QueryString);
context.Response.Redirect(redirectUrl, permanent: true);
return;
}
Expand Down