Merged PR 21497: [release/6.0] MSRC 68590 - newlines in domain literals

This add validation for embedded newlines in email addresses.
Based on https://dev.azure.com/dnceng/internal/_git/dotnet-runtime/pullrequest/20738
There is opt-in System.Net.Mail.EnableFullDomainLiterals switch to allow previous behavior

Author: Tomas Weinfurt

src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/EmailAddressAttribute.cs

@@ -7,6 +7,9 @@ namespace System.ComponentModel.DataAnnotations
         AllowMultiple = false)]
     public sealed class EmailAddressAttribute : DataTypeAttribute
     {
+        private static bool EnableFullDomainLiterals { get; } =
+            AppContext.TryGetSwitch("System.Net.AllowFullDomainLiterals", out bool enable) ? enable : false;
+
         public EmailAddressAttribute()
             : base(DataType.EmailAddress)
         {
@@ -27,6 +30,11 @@ public override bool IsValid(object? value)
                 return false;
             }
 
+            if (!EnableFullDomainLiterals && (valueAsString.Contains('\r') || valueAsString.Contains('\n')))
+            {
+                return false;
+            }
+
             // only return true if there is only 1 '@' character
             // and it is neither the first nor the last character
             int index = valueAsString.IndexOf('@');

src/libraries/System.ComponentModel.Annotations/tests/System/ComponentModel/DataAnnotations/EmailAddressAttributeTests.cs

@@ -29,6 +29,7 @@ protected override IEnumerable<TestCase> InvalidValues()
             yield return new TestCase(new EmailAddressAttribute(), 0);
             yield return new TestCase(new EmailAddressAttribute(), "");
             yield return new TestCase(new EmailAddressAttribute(), " \r \t \n" );
+            yield return new TestCase(new EmailAddressAttribute(), "someName@[\r\n\tsomeDomain]");
             yield return new TestCase(new EmailAddressAttribute(), "@someDomain.com");
             yield return new TestCase(new EmailAddressAttribute(), "@[email protected]");
             yield return new TestCase(new EmailAddressAttribute(), "someName");

src/libraries/System.Net.Mail/src/System/Net/Mail/MailAddress.cs

@@ -15,6 +15,9 @@ namespace System.Net.Mail
     //
     public partial class MailAddress
     {
+        private static bool EnableFullDomainLiterals { get; } =
+            AppContext.TryGetSwitch("System.Net.AllowFullDomainLiterals", out bool enable) ? enable : false;
+
         // These components form an e-mail address when assembled as follows:
         // "EncodedDisplayname" <userName@host>
         private readonly Encoding _displayNameEncoding;
@@ -219,6 +222,12 @@ private string GetHost(bool allowUnicode)
                     throw new SmtpException(SR.Format(SR.SmtpInvalidHostName, Address), argEx);
                 }
             }
+
+            if (!EnableFullDomainLiterals && domain.AsSpan().IndexOfAny('\r', '\n') >= 0)
+            {
+                throw new SmtpException(SR.Format(SR.SmtpInvalidHostName, Address));
+            }
+
             return domain;
         }
 

src/libraries/System.Net.Mail/tests/Functional/SmtpClientTest.cs

@@ -9,11 +9,15 @@
 // (C) 2006 John Luke
 //
 
+using System.Collections.Generic;
+using System.Globalization;
 using System.IO;
 using System.Net.NetworkInformation;
 using System.Net.Sockets;
+using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.DotNet.RemoteExecutor;
 using Systen.Net.Mail.Tests;
 using Xunit;
 
@@ -523,5 +527,60 @@ public async Task SendMail_SendQUITOnDispose(bool asyncSend)
             quitReceived.Wait(TimeSpan.FromSeconds(30));
             Assert.True(quitMessageReceived, "QUIT message not received");
         }
+
+        [ConditionalTheory(typeof(RemoteExecutor), nameof(RemoteExecutor.IsSupported))]
+        [InlineData("foo@[\r\n bar]")]
+        [InlineData("foo@[bar\r\n ]")]
+        [InlineData("foo@[bar\r\n baz]")]
+        public void MultiLineDomainLiterals_Enabled_Success(string input)
+        {
+            RemoteExecutor.Invoke(static (string @input) =>
+            {
+                AppContext.SetSwitch("System.Net.AllowFullDomainLiterals", true);
+
+                var address = new MailAddress(@input);
+
+                // Using address with new line breaks the protocol so we cannot easily use LoopbackSmtpServer
+                // Instead we call internal method that does the extra validation.
+                string? host = (string?)typeof(MailAddress).InvokeMember("GetAddress", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.InvokeMethod, null, address, new object[] { true });
+                Assert.Equal(input, host);
+            }, input).Dispose();
+        }
+
+        [Theory]
+        [MemberData(nameof(SendMail_MultiLineDomainLiterals_Data))]
+        public async Task SendMail_MultiLineDomainLiterals_Disabled_Throws(string from, string to, bool asyncSend)
+        {
+            using var server = new LoopbackSmtpServer();
+
+            using SmtpClient client = server.CreateClient();
+            client.Credentials = new NetworkCredential("Foo", "Bar");
+
+            using var msg = new MailMessage(@from, @to, "subject", "body");
+
+            await Assert.ThrowsAsync<SmtpException>(async () =>
+            {
+                if (asyncSend)
+                {
+                    await client.SendMailAsync(msg).WaitAsync(TimeSpan.FromSeconds(30));
+                }
+                else
+                {
+                    client.Send(msg);
+                }
+            });
+        }
+
+        public static IEnumerable<object[]> SendMail_MultiLineDomainLiterals_Data()
+        {
+            foreach (bool async in new[] { true, false })
+            {
+                foreach (string address in new[] { "foo@[\r\n bar]", "foo@[bar\r\n ]", "foo@[bar\r\n baz]" })
+                {
+                    yield return new object[] { address, "[email protected]", async };
+                    yield return new object[] { "[email protected]", address, async };
+                }
+            }
+        }
     }
 }