Super optimal

Author: DamianEdwards

src/Servers/Kestrel/Core/src/Internal/AddressBinder.cs

@@ -152,14 +152,12 @@ bool IsLocalhost(string host, out string? prefix)
             }
 
             // Check for use of .localhost TLD (Top Level Domain)
-            if (host.EndsWith(".localhost", StringComparison.OrdinalIgnoreCase))
+            if (host.EndsWith(".localhost", StringComparison.OrdinalIgnoreCase)
+                && !string.Equals(parsedAddress.Host, ".localhost", StringComparison.OrdinalIgnoreCase))
             {
-                if (host.LastIndexOf('.') > 0)
-                {
-                    // Take all but the .localhost TLD as the prefix
-                    prefix = host[..^10]; // 10 is the length of ".localhost"
-                    return true;
-                }
+                // Take all but the .localhost TLD as the prefix
+                prefix = host[..^10]; // 10 is the length of ".localhost"
+                return true;
             }
 
             prefix = null;