Handle CriticalExtensions and WeakSignature on 509Chain for macOS (#3…

…5548)

* Support unknown critical extensions on macOS.

If a certificate contains an unprocessable critical extension
in a certificate, map the "CriticalExtensions" status to
HasNotSupportedCriticalExtension instead of throwing an exception.

* Ignore WeakSignature chain status on macOS.

X509Chain on Windows will not check for modern signatures, so we
will let macOS do the same thing.

src/libraries/Native/Unix/System.Security.Cryptography.Native.Apple/pal_x509chain.c

@@ -176,12 +176,15 @@ static void MergeStatusCodes(CFTypeRef key, CFTypeRef value, void* context)
         *pStatus |= PAL_X509ChainRevocationStatusUnknown;
     else if (CFEqual(keyString, CFSTR("MissingIntermediate")))
         *pStatus |= PAL_X509ChainPartialChain;
+    else if (CFEqual(keyString, CFSTR("CriticalExtensions")))
+        *pStatus |= PAL_X509ChainHasNotSupportedCriticalExtension;
     else if (CFEqual(keyString, CFSTR("UnparseableExtension")))
     {
         // 10.15 introduced new status code value which is not reported by Windows. Ignoring for now.
     }
     else if (CFEqual(keyString, CFSTR("WeakLeaf")) || CFEqual(keyString, CFSTR("WeakIntermediates")) ||
-             CFEqual(keyString, CFSTR("WeakRoot")) || CFEqual(keyString, CFSTR("WeakKeySize")))
+             CFEqual(keyString, CFSTR("WeakRoot")) || CFEqual(keyString, CFSTR("WeakKeySize")) ||
+             CFEqual(keyString, CFSTR("WeakSignature")))
     {
         // Because we won't report this out of a chain built by .NET on Windows,
         // don't report it here.

src/libraries/System.Security.Cryptography.X509Certificates/tests/ChainTests.cs

@@ -1202,6 +1202,70 @@ public static void BuildChainForCertificateSignedWithDisallowedKey()
             }
         }
 
+        [Fact]
+        public static void BuildChainForCertificateWithMD5Signature()
+        {
+            byte[] issuerCert = Convert.FromBase64String(@"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");
+
+            byte[] md5SignedLeafCert = Convert.FromBase64String(@"
+MIIEezCCA2OgAwIBAgIUf1ubwalzwcn4DQ2X5hUbYPqateowDQYJKoZIhvcNAQEE
+BQAwfTELMAkGA1UEBhMCVVMxHTAbBgNVBAgMFERpc3RyaWN0IG9mIENvbHVtYmlh
+MRMwEQYDVQQHDApXYXNoaW5ndG9uMRAwDgYDVQQKDAdUZXN0IENBMRQwEgYDVQQL
+DAtEZXZlbG9wbWVudDESMBAGA1UEAwwJVGVzdCBSb290MCAXDTIwMDQyODAwNDI1
+OFoYDzIxMTYwMjI1MDA0MjU4WjBoMQswCQYDVQQGEwJVUzEdMBsGA1UECAwURGlz
+dHJpY3Qgb2YgQ29sdW1iaWExEDAOBgNVBAoMB1Rlc3QgQ0ExFDASBgNVBAsMC0Rl
+dmVsb3BtZW50MRIwEAYDVQQDDAlUZXN0IExlYWYwggEiMA0GCSqGSIb3DQEBAQUA
+A4IBDwAwggEKAoIBAQDGHz60IeCSpN1qQbdLHO2VSlQbOn2fBV5qGK/82+a4xiZf
+xO0wZ6p9Tb7/rOnF7P7YlaOrY9zc6O5vPxatcv2FcZxwrR8zDnslWUg39WzFnz4M
+8eiiGBpxlbUfcUq8FvqfGQ6MxMAwA0kgUjegaVXN1Zgq+J+HcLSJm8EADNOD46nS
+TkTVXvEMCBmrl17LyYEnxLogUgWve9QMNz0+XpJq90MlygPmxuvUnWduDGnVgrJq
+blkwFqaLIh94vmc8rQJ9WSy+1FRknDoDcy3KveYW3ii9uD9B7YvXdmFVEjGXPcUv
+9aFoRiqq/E8oYUhWJXTr9omyA3iJawcn0Kkl3IT7AgMBAAGjggEEMIIBADAJBgNV
+HRMEAjAAMCwGCWCGSAGG+EIBDQQfFh1PcGVuU1NMIEdlbmVyYXRlZCBDZXJ0aWZp
+Y2F0ZTAdBgNVHQ4EFgQUE9CCY2wzRzuH3lvEENkvBxDRFx8wgaUGA1UdIwSBnTCB
+mqGBgaR/MH0xCzAJBgNVBAYTAlVTMR0wGwYDVQQIDBREaXN0cmljdCBvZiBDb2x1
+bWJpYTETMBEGA1UEBwwKV2FzaGluZ3RvbjEQMA4GA1UECgwHVGVzdCBDQTEUMBIG
+A1UECwwLRGV2ZWxvcG1lbnQxEjAQBgNVBAMMCVRlc3QgUm9vdIIUZMWk1Y/+JyTi
+zhUIXUxp9Valav4wDQYJKoZIhvcNAQEEBQADggEBAGbrB50Gf9FQ1lTbtKQBlrpF
+M01/mHvqDioqjP6hcvDRMvxWcnX8kIq7Idb2uv1fByBPQdBTH2yzGc1adCXtBqrb
+ueIjvYVDoXZMqRa7vZjaMA+8szK9lgm2dzSfa3xFKCIT7Twfq6FKGJ7o4TRbopmr
+3MsjTMLjfGUnKdxtcYb/FGxB4NRdIyCaaRgtYOIFkOGgA3UTEAJuOAqwY8RdQywR
+lHBlkA0wrbydD3FzxYHUJgx0HGO6CcyAzXJLhZVbuBW4expq4Qhi0jDV4d8Otskv
+LjCvFGJ+RiZCbxIZfUZEuJ5vAH5WOa2S0tYoEAeyfzuLMIqY9xK74nlZ/vzz1cY=");
+
+            using (X509Certificate2 issuer = new X509Certificate2(issuerCert))
+            using (X509Certificate2 cert = new X509Certificate2(md5SignedLeafCert))
+            using (ChainHolder chainHolder = new ChainHolder())
+            {
+                X509Chain chain = chainHolder.Chain;
+                chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
+                chain.ChainPolicy.VerificationTime = cert.NotBefore.AddHours(2);
+                chain.ChainPolicy.ExtraStore.Add(issuer);
+
+                // Should not throw, don't care about the validity of the chain.
+                chain.Build(cert);
+            }
+        }
+
         internal static X509ChainStatusFlags AllStatusFlags(this X509Chain chain)
         {
             return chain.ChainStatus.Aggregate(

src/libraries/System.Security.Cryptography.X509Certificates/tests/DynamicChainTests.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Linq;
 using System.Runtime.InteropServices;
 using Test.Cryptography;
 using Xunit;
@@ -281,6 +282,42 @@ public static void BasicConstraints_ViolatesCaFalse()
             }
         }
 
+        [Fact]
+        public static void TestLeafCertificateWithUnknownCriticalExtension()
+        {
+            using (RSA key = RSA.Create())
+            {
+                CertificateRequest certReq = new CertificateRequest(
+                    new X500DistinguishedName("CN=Cert"),
+                    key,
+                    HashAlgorithmName.SHA256,
+                    RSASignaturePadding.Pkcs1);
+
+                const string PrecertificatePoisonExtensionOid = "1.3.6.1.4.1.11129.2.4.3";
+                certReq.CertificateExtensions.Add(new X509Extension(
+                    new AsnEncodedData(
+                        new Oid(PrecertificatePoisonExtensionOid),
+                        new byte[] { 5, 0 }),
+                    critical: true));
+
+                DateTimeOffset notBefore = DateTimeOffset.UtcNow.AddDays(-1);
+                DateTimeOffset notAfter = notBefore.AddDays(30);
+
+                using (X509Certificate2 cert = certReq.CreateSelfSigned(notBefore, notAfter))
+                using (ChainHolder holder = new ChainHolder())
+                {
+                    X509Chain chain = holder.Chain;
+                    chain.ChainPolicy.RevocationMode = X509RevocationMode.NoCheck;
+                    Assert.False(chain.Build(cert));
+
+                    X509ChainElement certElement = chain.ChainElements.OfType<X509ChainElement>().Single();
+                    const X509ChainStatusFlags ExpectedFlag = X509ChainStatusFlags.HasNotSupportedCriticalExtension;
+                    X509ChainStatusFlags actualFlags = certElement.AllStatusFlags();
+                    Assert.True((actualFlags & ExpectedFlag) == ExpectedFlag, $"Has expected flag {ExpectedFlag} but was {actualFlags}");
+                }
+            }
+        }
+
         [Fact]
         public static void TestInvalidAia()
         {